Chapter Eight


by Lawrence W. Sherman

The more police we have, the less crime there will be. While citizens and public officials often espouse that view, social scientists often claim the opposite extreme: that police make only minimal contributions to crime prevention in the context of far more powerful social institutions, like the family and labor markets. The truth appears to lie in between. Whether additional police prevent crime may depend on how well they are focused on specific objectives, tasks, places, times and people. Most of all, it may depend upon putting police where serious crime is concentrated, at the times it is most likely to occur: policing focused on risk factors.

The connection of policing to risk factors is the most powerful conclusion reached from three decades of research. Hiring more police to provide rapid 911 responses, unfocused random patrol, and reactive arrests does not prevent serious crime. Community policing without a clear focus on crime risk factors generally shows no effect on crime. But directed patrols, proactive arrests and problem-solving at high-crime "hot spots" has shown substantial evidence of crime prevention. Police can prevent robbery, disorder, gun violence, drunk driving and domestic violence, but only by using certain methods under certain conditions.

These conclusions are based largely on research supported by the National Institute of Justice, the research arm of the Office of Justice Programs in the U.S. Department of Justice. In recent years, increasing numbers of police executives have incorporated these findings into their crime prevention strategies. University of Wisconsin law professor Herman Goldstein's (1979) paradigm of "problem-oriented policing" directed research attention to the specific things police do, and how they can focus their resources to attack the proximate causes of public safety problems. The Justice Department's adoption of this perspective has yielded an increasingly complex but useful body of knowledge about how policing affects crime.

One of the most striking recent findings is the extent to which the police themselves create a risk factor for crime simply by using bad manners. Modest but consistent scientific evidence supports the hypothesis that the less respectful police are towards suspects and citizens generally, the less people will comply with the law. Changing police "style" may thus be as important as focusing police "substance." Making both the style and substance of police practices more "legitimate" in the eyes of the public, particularly high-risk juveniles, may be one of the most effective long-term police strategies for crime prevention.

This chapter begins with a review of the eight major hypotheses about how the police can prevent crime (Figure 1). It then describes the varying strength of the scientific evidence on those hypotheses, in relation to the "rigor" of the scientific methods used to test them. The available studies are summarized for both their conclusions and their scientific rigor. The chapter then attempts to simplify these results by answering the questions about what works, what doesn't, and what's promising. Major gaps in our knowledge are also examined. The chapter concludes with recommendations derived from these findings for future federal investment in both evaluation research and police methods to be developed for evaluation.

Figure 8-1

Eight Major Hypotheses About Policing and Crime

Other things being equal,

1. Numbers of Police. The more police a city employs, the less crime it will have.

2. Rapid Response to 911. The shorter the police travel time from assignment to arrival at a crime scene, the less crime there will be.

3. Random Patrols. The more random patrol a city receives, the more a perceived "omnipresence" of the police will deter crime in public places.

4. Directed Patrols. The more precisely patrol presence is concentrated at the "hot spots" and "hot times" of criminal activity, the less crime there will be in those places and times.

5. Reactive Arrests. The more arrests police make in response to reported or observed offenses of any kind, the less crime there will be.

6. Proactive Arrests. The higher the police-initiated arrest rate for high-risk offenders and offenses, the lower the rates of serious violent crime.

7. Community Policing. The more quantity and better quality of contacts between police and citizens, the less crime.

8. Problem-Oriented Policing. The more police can identify and minimize proximate causes of specific patterns of crime, the less crime there will be.


1. Numbers of Police. Like the deterrence hypothesis itself (Gibbs, 1975), the claim that police prevent crime is not a "theory" in a truly scientific sense. The idea was developed not as a mathematical equation but as a general "doctrine" of public policy in the heat of democratic debate. The doctrine was based not just on speculation, but also on the apparent results of several "demonstration projects" with some empirical results. These included the court supervised "Bow Street Runners" (Lee, 1901 [1971]; Pringle, 1955) and the privately operated but publicly chartered Thames River "Marine Police" (Stead, 1977). As the level of violence throughout the 19th century declined while the number of police increased (Gurr, et al, 1977: 93-96; 140), many observers concluded that the more police, the less crime.

2. Rapid Response to 911. The general form of this claim is that the shorter the police travel time from assignment to arrival at a crime scene, the more likely it is that police can arrest offenders before they flee. This claim is then extended to rapid response producing three crime prevention effects. One is a reduction in harm from crimes interrupted in progress by police intervention. Another, more general benefit of rapid response time is a greater deterrent effect from the threat of punishment reinforced by response-related arrests. The third hypothesized prevention effect comes from the incapacitation through imprisonment of offenders prosecuted more effectively with evidence from response-related arrests. All of these claims presume, of course, that police are notified during or immediately after the occurrence of a crime. This premise, like the hypotheses themselves, is empirically testable, and it's falsification could logically falsify the hypotheses built upon the assumption of its validity.

3. Random Patrols. Early beat officers were directed to check in at specific places at specific times, with rigid supervision of the prescribed patrol patterns (Reiss, 1992). The increasing emphasis on rapid 911 response in automobiles gradually put an end to directed patrols, allowing officers to patrol at random far beyond their assigned beats. This policy was justified by the theory that unpredictability in patrol patterns would create a perceived "omnipresence" of the police that deters crime in public places. Chicago Police Chief and Berkeley Criminology Dean Orlando W. Wilson (1963: 232) was a widely cited proponent of this view. Although he favored the use of police workload analysis to determine how many officers should be assigned to different beats and shifts, modern police practice shows little variation in patrol presence by time and place. Nonetheless, many police chiefs and mayors claim that hiring more officers to patrol in this fashion would reduce crime.

4. Directed Patrols. Since the advent of computerized crime analysis, however, a far greater precision in the identification of crime patterns has become possible. Police have used that precision to focus patrol resources on the times and places with the highest risks of serious crime. The hypothesis is that the more patrol presence is concentrated at the "hot spots" and "hot times" of criminal activity, the less crime there will be in those places and times. The epidemiological underpinning for this claim is NIJ-funded research showing that the risk of crime is extremely localized, even within high crime neighborhoods, varying widely from one address to another (Pierce, Spaar and Briggs, 1988; Sherman, Gartin and Buerger, 1989).

5. Reactive Arrests. Like police patrol, arrest practices can be either unfocused or focused on crime-risk factors. Reactive arrests (in response to specific citizen complaints) are like random patrol in that they cast a wide net, warning all citizens that they can be arrested for all law violations at all times. This net is necessarily quite thin. Observations of thousands of police encounters with criminal suspects shows that police choose not to arrest suspects in the majority of the cases in which there was legal basis to do so (Black, 1980: 90; Smith and Visher, 1981: 170). The frequent decision not to arrest has been noticed by crime victims' advocacy groups, who argue that more arrests will produce less crime. This hypothesis, like deterrence generally, is expressed at two levels of analysis: the "general" or community-wide, and the "specific" or individual-level. The individual-level hypothesis has been questioned for decades by social scientists, and even some police, who suggest exactly the opposite: that arrest, especially for minor offenses (which are by far the most common), provokes a response by offenders making them more likely to commit future crime than if they had not been arrested.

6. Proactive Arrests. Like directed patrol, proactive (police-initiated) arrests concentrate police resources on a narrow set of high-risk targets. The hypothesis is that a high certainty of arrest for a narrowly defined set of offenses or offenders will accomplish more than low arrest certainty for a broad range of targets. In recent years the theory has been tested with investigations of four primary high risk targets: chronic serious offenders, potential robbery suspects, drug market places and areas, and high-risk places and times for drunk driving. All but the first can be tested by examining the crime rate. The hypothesis about chronic serious offenders is tested by examining the rate at which such offenders are incapacitated by imprisonment from further offending.

Another version of the proactive arrest hypothesis is called "zero tolerance," based on the "broken windows" theory (Wilson and Kelling, 1982). The theory is that areas appearing disorderly and out-of-control provide an attractive climate for violent crime--just as a window with one broken pane attracts more stones than a completely unbroken window. The crime prevention hypothesis is that the more arrests police make for even petty disorder), the less serious crime there will be (Skogan, 1990).

Community vs. Problem-Oriented Policing

The hypotheses about community- and problem-oriented-policing are less focused than the others, so much so that some observers have even advised against trying to test them (Moore 1992: 128). They both involve far more variations and possible combinations of police activities than the narrow deterrence hypotheses. As in the community- and school-based programs reviewed in chapters 2 and 4, community and problem-oriented policing are put into practice more like a "stew" of different elements than a single type of "food." Yet it is just this flexibility that proponents hypothesize to give them their power. Crime problems vary so widely in nature and cause that effective policing for prevention must vary accordingly, and arguably require many elements to succeed.

While community and problem-oriented policing are often said to be overlapping strategies (Skogan, 1990; Moore, 1992), they actually have very different historical and theoretical roots. Community policing arises from the crisis of legitimacy after the urban race riots of the 1960s, the proximate causes of which several blue-ribbon reports blamed on police (President's Commission on Law Enforcement and Administration of Justice, 1967; National Advisory Commission on Civil Disorders, 1968). The reports claimed police had lost contact with minority group residents, both by changing from foot patrols to radio cars and by taking a more legalistic approach to law enforcement. In various ways, most notably "team policing" (Task Force Report; Sherman, et al 1973), the police were urged to increase their contact with citizens in more positive settings than just responding to emergencies. Thus for almost three decades the Community Policing hypothesis has been that increasing the quantity and quality of police-citizen contact (Kelling, 1988) reduces crime.

Problem-oriented policing, in contrast, arose from the crisis of police effectiveness at crime prevention provoked in the 1970s by some of the very studies reviewed in this chapter. As one of its early sponsors, Gary Hayes (1979), put it, the studies told police chiefs that nothing they were doing--putting more police on the street into random patrols, rapid responses--was working to fight crime. The strategy of problem-oriented policing conceived by Professor Goldstein (1979) provided a new paradigm in which to focus innovation, regardless of any contact with the citizenry. Where the core concept of community policing was community involvement for its own sake, the core concept for problem-oriented policing was results: the effect of police activity on public safety, including (but not limited to) crime prevention. Nonetheless, community policing has also been justified by its hypothesized effects on crime, not the least of which has been the rationale for the 100,000 federally funded police officers.

7. Community Policing. The crime prevention effects of community policing are hypothesized to occur in four major ways.

7.a. Neighborhood Watch. This hypothesis justifies one of the most widespread community policing programs, "block watch": increasing volunteer surveillance of residential neighborhoods by residents, which should deter crime because offenders know the neighbors are watching.

7.b. Community-Based Intelligence. This hypothesis justifies the many community meetings (Sherman et al, 1973) and informal contacts police sought through storefront offices, foot patrol (Trojanowicz, 1986) and other methods: increasing the flow of intelligence from citizens to police about offenses and offenders, which then increases the probability of arrest for crime and the deterrent incapacitative effects of arrest. The increased flow of citizen intelligence can also increase police effectiveness at crime prevention through problem-solving strategies.

7.c. Public Information About Crime. This hypothesis is just the reverse of the last one: increased flow of police intelligence about crime back to citizens improves citizen ability to protect themselves, especially in light of recent changes in crime patterns and risks. The latest version of this idea is "reverse 911," under which police fax out warnings of criminal activity to a list of residential and business fax numbers requesting the service.

7.d. Police Legitimacy. Given the historical roots of community policing, perhaps the most theoretically compelling version of its crime prevention hypothesis addresses police legitimacy, or public confidence in the police as fair and equitable (Eck and Rosenbaum, 1994). Recent theoretical and basic research work in "procedural justice" (Tyler, 1990) provides a more scientifically elaborate version of this hypothesis than its proponents in the 1960s intended. The claim is not just that police must be viewed as legitimate in order to win public cooperation with law enforcement. The claim is that a legitimate police institution fosters more widespread obedience of the law itself. Gorer (1955: 296) even attributes the low levels of violent crime in England to the example of law-abiding masculinity set by 19th Century police, a role model that became incorporated into the "English character." There is even evidence that the police themselves become less likely to obey the law after they have become disillusioned with its apparent lack of procedural justice (Sherman, 1974).

8. Problem-Oriented Policing offers infinite specific hypotheses about crime prevention, all under this umbrella claim: the more accurately police can identify and minimize proximate causes of specific patterns of crime, the less crime there will be. In recent years this claim has taken two major forms:

8.a. Criminogenic Commodities. The more police can remove criminogenic substances from the micro-environments of criminal events, the fewer crimes there will be. This claim arises from the growing emphasis on the causation of criminal events as partly independent of the causation of individual criminality (Hirschi, 1986). Like the theories about preventing crime in places (Chapter 7), the premise is that many crimes require certain preconditions, such as guns or cash or moveable property (Cohen and Felson, 1979).

8.b. Converging Offenders and Victims. Another precondition of violent criminal events is that victims and offenders must intersect in time and space. A major problem-solving theory of crime prevention is to keep the more basic elements of criminal events from combining: the more police can reduce the intersection of motivated offenders in time and space with suitable targets of crime, the less crime there will be.


All of these hypotheses pose formidable challenges to scientific testing. The measurement of crime is difficult under any circumstances, let alone in relation to experiments or natural variation in police practices. Control over police practices is difficult for police administrators under normal conditions, let alone under experimental protocols. Measuring the many dimensions of police activity, from effort to manners, is expensive and often inaccurate. Only a handful of studies have managed to produce strong scientific evidence about any of these hypotheses. But the accumulated evidence of the more numerous weaker studies can also provide some insights on policing for crime prevention.

As noted in chapter 1, this report employs a scale of 1 to 5 to summarize several different dimensions of scientific "rigor": the strength of scientific evidence. A score of 5 = strongest evidence for inferring cause and effect, while 1 = the weakest. These dimensions vary somewhat by institutional setting, with different issues inherent in the kinds of programs being evaluated. problems. In the police evaluation literature, crime is almost always measured by either official crime reports (with all their flaws) or by victimization surveys of the public (with all their costs). Police practices are measured either not at all, through citizen perceptions of those practices, through police records, or (in one instance) through direct observation of police patrol activity. It is not clear that any of these methods except the last is superior to any others in drawing valid inferences about the actual practices of the police. Thus the greatest difference across police evaluations lies not in their methods of measurement, but in their basic research designs: the logical structure for drawing conclusions about cause and effect.

Evaluations of police crime prevention generally follow five basic research designs, which can be ranked for overall strength of the inferences they can suggest about cause and effect. These designs are 1) correlations at the same point in time (e.g., in 1995 the cities with the most police had the most crime) 2) before-and-after differences in crime without a comparison group (e.g., doubling drunk driving arrests was followed by a 50% reduction in fatal accidents, 3) before-after differences with comparison (e.g., the 50% reduction in fatal crashes compared to a 10% increase in fatal crashes in three cities of comparable size in the same state), 4) before and after large sample comparisons of treated and untreated groups (e.g., 30 neighborhoods organized for neighborhood watch compared to 30 that were not), and 5) randomized controlled experiments (300 offenders selected by a computerized equal probability program to be arrested had higher repeat offending rates than 300 offenders selected to be given warnings only).


This section reviews and interprets the reported tests of each of the hypotheses. The discussion attempts to integrate both the scientific score of the various studies and the number of studies converging on the same conclusion. More detailed discussion is offered for some of the major findings, in order to connect the evidence more clearly to the hypotheses. The main concern throughout this section is the cumulative success or failure of the studies in ruling out competing theories in the attempt to provide a conclusive test of each hypothesis.

1. Numbers of Police

As Table 1 shows, most of the studies of the effects of police numbers on crime are scientifically weak. They consist of two basic research designs. One is evidence from police strikes1 about a sudden and drastic reduction in police numbers. The other is evidence from correlational studies of police strength and crime rates.

The police strike evidence, while weak in both measurement and design, is fairly consistent in showing the effect of this natural experiment: crime rates skyrocket instantly. The strongest design is the Makinen and Takala (1980) study of crime in Helsinki before and during a police strike. The Helsinki measures included systematic observation counts of fights in public places, as well as emergency room admissions for assault-related injuries. Both measures rose substantially during the strike despite severe winter weather. The only purportedly negative evidence on this conclusion is the Pfuhl (1983) study of police-recorded crime in 11 American police strikes, in which 89% of the "strike" period in the analysis consisted of non-strike days. Both the measure and the definition of the strike period hopelessly confound cause and effect, rendering the study irrelevant to the conclusion reached from the stronger evidence.

None of the strike findings have comparison groups, so in theory it is possible that crimes would have risen dramatically during the strike period even without the strike. The substantial magnitudes of some of the increases, however, greatly exceed typical daily variations in crime in big cities. In the Montreal police strike of 1969, for example, there were 50 times more bank robberies and 14 times more commercial burglaries than average (Clark, 1969). Thus despite the weak research design, the large effect size suggests that abolishing a police force can cause crime to increase.

Table 8-1: Numbers of Police

The more police a city employs, the less crime it will have.

Studies                      Scientific Methods Score     Findings                      

Andenaes 1974                2                            1944 No Danish Police,        
                                                          large robbery & larceny       

Clark 1969                   2                            Police Strike, major          
                                                          increase in violent &         

Russell 1975                 2                            Same as preceding (Boston)    

Sellwood 1978                2                            Same as preceding             

Makinen and Takala 1980      2                            Same as preceding (Helsinki)  

Pfuhl 1983                   1                            No crime increase during      
                                                          quarters with police strike   

Marvell & Moody 1996         3                            Higher police numbers in      
                                                          cities reduce most types of   

          36 study review    2                            Little evidence that more     
                                                          police reduce crime; weak     

Whether adding more officers to an already large police force causes crime to decrease, however, is somewhat less clear. A recent review of 36 correlational studies, most of them weak in research design, found little evidence that more police reduce crime (Marvell and Moody, 1996). The same authors, however, offer a twenty-year analysis of 56 cities of over 250,000 people each and of 49 states. Using a complex technique called the Granger test, Marvell and Moody (1996) find consistent evidence that increases in the numbers of police cause reductions in crime in the following year. This study rates a level 4 because it employs multiple comparison groups and uses appropriate controls for well-specified differences across units. While it lacks random assignment, it is the best evidence available about the effect of modest increases in police numbers. While it runs against the conclusion of the preponderance of the other studies, the difference in scientific rigor tips the preponderance of the evidence in the direction of the conclusion that police numbers alone do help to reduce crime in a big city or a state. What the causal mechanism for that effect may be or how it may be enhanced, however, is not clear.

The Marvell and Moody (1996: 632) analysis also allows a test of the hypothesis that the prevention benefits of hiring more police officers are greater in higher-crime cities than across the country in general. The analysis estimates that for each additional officer added to a police force in a big city, 24 Part I crimes are prevented annually. For each officer hired anywhere in a state, only 4 Part I crimes are prevented. States, on average, have much lower crime rates than the big cities (over 250,000 population); in 1995 the rate of Part I crimes was 8,563 per 100,000 in the big cities, compared to 5,624 per 100,000 across all police agencies. Yet the ratio of crime prevention benefit is far greater than the ratio of reported crime risks. The Marvell and Moody estimate shows that six times as much crime is prevented for each officer added in cities than added in all places on average. Why the benefit ratio exceeds the risk ratio is unknown, but one likely candidate is the greater population density in cities which lets additional police officers have greater effects on patrol visibility per resident.

2. Rapid Response to 911

One major theory about the crime prevention benefits of hiring more officers is that it reduces police response time. The research on this theory is an excellent example of how different conclusions can result from research results with very different levels of scientific strength. The initial studies of the response time hypothesis produced strong support, suggesting that shaving minutes off response time could lead to the arrest of many more offenders. The extension of this hypothesis into a strategy of policing included the development of 911 systems to speed victim contact with police radio dispatchers, and the hiring of more police nationwide in the early 1970s in order to reduce average response times and deter crime through greater certainty of arrest. Only the 1977 NIJ response time analysis in Kansas City study, and the NIJ replications in four other cities, were able to call that strategy into question, and open the door to more focused alternatives (Goldstein, 1979).

The original test of the hypothesis was based on a scientifically weak research design, a non-random sample of 265 police responses to citizen calls by the Los Angeles Police Department (Isaacs, 1967). Its results were confirmed by a later study in Seattle (Clawson and Chang, 1977): the probability of arrest per police response increased as police time in travel to the scene decreased. Two other studies (Brown, 1974; Holliday, 1974, as cited in Chaiken, 1978) failed to find that pattern, perhaps because, as Chaiken (1978: 130) observes, "the curves are essentially flat for response times larger than three minutes, and therefore a substantial amount of data for responses under three minutes is needed to observe any effect."

The Kansas City (1977) response time analysis took a far more systematic approach to the issue. Its first step was to divide crimes into victim-offender "involvement" (e.g., robbery, assault, rape) and after-the-crime "discovery" categories (e.g., burglary, car theft). It then focused response time analysis on involvement crimes, since the offender would not be present at the discovery crimes. The analysis then divided the involvement crime "response time" into three time periods: crime initiation to calling the police ("reporting time"), police receipt of call to dispatch ("dispatch time"), and "travel time" of police from receipt of dispatch to arrival at the scene. Using systematic observation methods and interviews of victims, the Kansas City study (1977, Vol. 2: 39) found that

Table 8-2: Rapid Response

The shorter the police travel time from assignment to arrival at a crime scene, the less crime there will be.

Studies                      Scientific Methods Score     Findings                      

Isaacs 1967                  1                            Shorter police travel time,   
                                                          more arrests                  

Clawson and Chang 1977       1                            Same as preceding             

Pate et al 1976              1                            Police travel time unrelated  
                                                          to arrest                     

Kansas City (MO) Police      2                            Same as preceding, most       
1977                                                      crimes                        

Spelman and Brown 1981       2                            Same as preceding             

there was no correlation between response-related arrest probability and reporting time once the time exceeded 9 minutes. The average reporting time for involvement crimes is 41 minutes (K.C.P.D. 1977, Vol. 2: 23). Cutting police travel time for such crime from 5 to 2.5 minutes could require a doubling of the police force, but it would have almost no impact on the odds of making an arrest.

Police chiefs in the Police Executive Research Forum (PERF) told NIJ that they did not think citizens in their own communities would take so long to call the police. NIJ responded by commissioning PERF to replicate the citizen reporting component of the response time analysis in four other cities. Over 4,000 interviews about 3,300 "involvement" crimes produced unequivocal support for the findings of the Kansas City response time analysis (Spelman and Brown, 1981). The probability of arrest in those serious crimes was only 29 per 1,000 reports, with 75% of serious crimes being discovered by victims long after the crimes occurred. Of the 25% that directly involved the victims, almost half were reported five minutes or more after the crime was completed. The findings were consistent across cities, including one that had a 911 system and three that did not.

The conclusion that reduced response time will not reduce crime is based on strong but indirect evidence. The evidence is strong because it is based on large samples, careful measurement, and a replicated research design in five diverse cities showing little variation in arrest rates by police travel time, the main factor that tax dollars can affect. It is indirect because an experimental test of the effects of reduced police travel time on city-wide arrest and crime rates has never been conducted. Yet there is neither empirical nor theoretical justification for such an expensive test. Given the strong evidence of citizen delays in reporting involvement crimes, and the small proportion of serious crimes that feature direct victim-offender involvement, further tests of this theory seem to be a waste of tax dollars. Those dollars might be better spent on communicating the findings to the general public, which still puts great priority on police travel time for public safety (Sherman, 1995).

3. Random Patrols

Another major theory about the benefits of more police is that they can conduct more random patrols. Table 3 summarizes the evidence for the police numbers hypothesis tested at the level of uniformed patrols within cities, in non-directed or random patrol patterns. The Table shows weak evidence of no effect of moderate variations in numbers or method of patrols. The most famous test of the random preventive patrol hypothesis, the Kansas City Preventive Patrol Experiment (Kelling et al, 1974), reveals some of the difficulty in testing this claim. This experiment claimed to have varied the dosage of patrol presence for one year across three groups of five randomly assigned beats each, preceded and followed by extensive measures of crime from both household surveys and official records. The results of the experiment showed no statistically significant differences in

Table 8-3: Random Patrol

The more random patrol a city receives, the more a perceived "omnipresence" of the police deters crime in public places.

Studies                      Scientific Methods Score     Findings                      

Kelling et al 1974           3                            No difference in crime by N   
                                                          of police cars assigned       

Police Foundation 1981       3                            No difference in crime by N   
                                                          of foot patrol assigned       

Trojanowicz 1986             3                            Foot patrol areas had fewer   
                                                          crimes than controls, but no  
                                                          significance tests reported.  

crime across the three groups.

Many criminologists conclude from this experiment that there is no crime prevention effect of adding patrol presence in a big city, where low density of crime makes the extra patrol a mere drop in the bucket (Felson, 1994). Yet the experiment has been criticized for its failure to measure the actual differences in patrol dosage and the possible lack of them (Larson, 1975), its inadequate statistical power to detect large percentage differences in crime as not due to chance (Fienberg, et al, 1976), and its failure to assign patrol dosage at random (Farrington, 1982). Similar limitations are found in the Newark Foot Patrol Experiment (Police Foundation, 1981), where despite large victimization surveys no crime prevention effects were detected in association with adding or eliminating daytime and early evening foot patrols from selected patrol beats.

The weakness of the evidence is even greater for the one study claiming to find a crime prevention effect from random patrols not focused on crime risks (Trojanowicz, 1986). The design of this study was limited to recorded crime and calls for service, with no victimization surveys. After daytime foot patrols were added to 14 beats in Flint Michigan for three years, the official crime counts in those beats were down by 9% in the foot patrol beats and up 10% in the other beats city-wide. Large increases in burglary and robbery in the foot patrol areas were matched by reportedly greater increases in the rest of the city. No significance tests were reported, nor were there any controls for the demographic characteristics of the areas selected for foot patrol compared to the rest of the city. Since the foot patrol areas were not selected at random, it is possible that those areas might have experienced different crime trends even without the foot patrols. The fact that the increase in burglary and robbery occurred largely at night when the foot patrols were not working is perhaps the most interesting fact in the study, supporting the conclusion reached from evaluations of directed patrols focused on high crime-risk times and places.

4. Directed Patrols

The evidence from the directed preventive patrol hypothesis is more voluminous, scientifically stronger (in two tests), and consistently in the opposite direction from the weight of the (weak) evidence on the random patrol hypothesis. In order to be assigned to this category, the studies had to indicate that they were somehow focused on high-crime places, times or areas. In the New York City study (Press, 1971: 94), for example, the test precinct was known as a high robbery area, and had over three times as many robberies per week as each group of five areas in the Kansas City experiment. All eight of the reported tests of this hypothesis show crime reductions in response to increased patrol presence.

Table 8-4 Directed Patrol

The more precisely patrol presence is concentrated at the "hot spots" and "hot times" of criminal activity, the less crime there will be in those places and times.

Studies                      Scientific Methods Score     Findings                      

Press 1971                   3                            40% more police, reductions   
                                                          of outdoors crime             

Chaiken et al 1975; Chaiken  3                            Police on subways at night    
1978                                                      reduced crime                 

Dahman 1975                  2                            More police, reductions of    
                                                          outdoors crime                

Schnelle et al 1977          2                            400% more patrol, less Part   
                                                          I crime                       

Sherman and Weisburd 1995    5                            100% more patrol, less        
                                                          observed hot spot crime       

Koper 1995                   4                            Longer patrol visits, longer  
                                                          post-visit crime-free time    

Reiss 1995 Review:                                                                      
     Barker et al 1993       2                            Squad focused on hot spots,   
                                                          where street crime dropped    
     Burney 1990             2                            Saturation patrols, reduced   
                                                          street crime                  

The crime prevention effects of extra uniformed patrol in marked police cars at high crime "peaks" are especially evident in two very different research designs imposed on one large NIJ study designed to improve upon the Kansas City Preventive Patrol Experiment. Based on the NIJ-funded research showing extreme concentrations in spatial and temporal distributions of crime, the Minneapolis Police Department (MPD) reorganized its entire patrol force in 1988-89 to test a pattern of directed patrols at hot spots during hot times. With the unanimous consent of the City Council, the MPD substantially reduced patrols from low-crime areas in order to provide 2 to 3 hours of extra patrol each day during high crime hours at 55 street corner hot spots. The corners were randomly selected for extra patrols from a carefully compiled list of 110 high crime locations that were visually separate from each other (Buerger, Petrosino and Cohn, 1995). Under a million dollar NIJ grant, both the patrolled and unpatrolled hot spots were subjected to over 7,000 randomly selected hours of observations by independent researchers over the course of a year. The observers recorded every minute of 24,813 instances of police presence in the hot spots, and 4,014 observed acts of crime and disorder (Koper, 1995: 656).

Koper's (1995) analysis of the Minneapolis Hot Spots Patrol data found a very strong relationship between the length of each police patrol presence (which averaged 14 minutes) and the amount of time the hot spot was free of crime after the police left the scene. The longer the police stayed before they left, the longer the time until the first crime (or disorderly act) after they left. This relationship held for each additional minute of police presence from one to fifteen minutes, after which the relationship began to reverse. Thus the "Koper curve" in the Minneapolis data suggests the optimum length of a police patrol visit to a hot spot for the purpose of deterring crime is about 15 minutes.

Koper's correlational analysis of all police presences observed in both the extra-patrol and no-extra-patrol hot spots combined is consistent with the results of Sherman and Weisburd's (1995) comparisons of the two groups. The experimental analysis found that there was an average of twice as much patrol presence and up to half as much crime in the extra-patrol hot spots as in the no-extra-patrol group. The observational data showed crime or disorder in 4 percent of all observed minutes in the control group compared to 2 percent in the experimental group (Sherman and Weisburd, 1995: 64). Most of the difference in the observed crime was found when police were not present in the hot spots. Crime-related calls for service increased for both groups of hot spots over the one-year experiment as well as city-wide, but the average growth per hot spot was up to three times as great in the no-extra-patrol group (17%) as in the extra patrol group (5%) (Sherman and Weisburd, 1995: 644).

These findings can be questioned, like most place-linked crime prevention effects, with the possible side effect that the crime simply moved elsewhere (but see the discussion of displacement in Chapter Seven). So, too, can a reduction of crime in one city be questioned on the grounds that offenders may have focused on other jurisdictions. The theoretical perspective of "routine activities" (Cohen and Felson, 1979; Felson, 1994), under which crimes are only likely to happen in certain places and times, makes the displacement hypothesis less plausible. It suggests that if crime is displaced, it would have to be displaced to other hot spots. That argument is still consistent with the experimental-comparison group analysis, given the rising numbers of calls in the experimental year relative to the baseline year. But it does not explain away Koper's cross-sectional analysis of the effects of longer patrol presence on post-patrol crime rates.

5. Reactive Arrests

The evidence in support of the reactive arrest hypothesis is remarkably unencouraging at both the community and individual levels of analysis. As a matter of general deterrence, the tests are all fairly weak and generally negative. As a matter of individual deterrence, the results are consistently negative for juveniles, and contradictory for two different groups of domestic assailants, employed an unemployed. The scientific evidence for the latter is among the strongest available in the police literature, while the evidence about juveniles is much weaker. Taken as a whole, these results make a vivid demonstration of the complexity of police effects on crime.

The evidence on the general deterrent effects of reactive (Reiss, 1971) arrests is based on correlational analyses, with and without temporal order. There is some weak evidence that there is a threshold beyond which the effect of increased arrest rates becomes evident, while no such effect is apparent below the "tipping point" of minimum dosage level (Tittle and Rowe, 1974). This evidence is complicated by the suggestion that the arrest effects are only evident among cities of less than 10,000 people, even with the "tipping point." The finding by Greenberg and his colleagues (1979, 1982) of no arrest rate deterrent effects in a temporal sequence design in big cities throws great doubt on a simple claim of general deterrence. Here again, without focusing arrests on high risk persons or places, the effects of higher arrest levels may get lost in the many factors causing crime.

Table 8-5 Reactive Arrests

The more arrests police make in response to reported or observed offenses of any kind, the less crime there will be.

5.a. General Deterrence. The higher the arrest rate per crime for each type of crime in a city, the lower the city's rate of that type of crime.

Studies                      Scientific Methods Score     Findings                      

Tittle and Rowe 1974         2                            Cities with higher arrest     
                                                          rates beyond a "tipping       
                                                          point" have less crime, but   
                                                          under tip point no arrest     

Logan 1975                   2                            No correlation of arrest      
                                                          rates and crime across        

Brown 1978                   2                            Tipping effect limited to     
                                                          cities under 10,000 people    

Greenberg et al 1979         2                            No effect of arrest rates on  
                                                          crime across cities           

Greenberg and Kessler 1982   3                            No arrest rate effect even    
                                                          when other factors            

Chamlin 1988                 3                            More arrests reduce           
                                                          robberies, not 4 property     

Chamlin 1991                 3                            No arrest rate effect for     
                                                          cities over 10,000            

5.b. Specific Deterrence. Individual offenders arrested for an offense are less likely to repeat that offense in the future than offenders who are not arrested.

Table 8-5b: Specific Deterrence

Studies                      Scientific Methods Score     Findings                      

Juvenile Offenses:                                                                      

Gold and Williams 1970       2                            Arrested juveniles offend     
                                                          more post-arrest than those   
                                                          not arrested                  

Klein 1986                   4                            More formal arrest            
                                                          processing increased          

Huizinga and Esbensen 1992   2                            Same as preceding             

Smith and Gartin 1989        2                            Arrested juveniles offend     
                                                          less post-crime than those    
                                                          not arrested, if they are     
                                                          first offenders; others more  

Farrington 1977              2                            Arrested juveniles offend     
                                                          more post-arrest than those   
                                                          not arrested                  

Domestic Violence                                                                       

Sherman and Berk 1984        4                            Arrest reduced recidivism     

Dunford et al 1990           5                            Arrest had no effect on       
                                                          recidivism at 6 mos           

Dunford 1992                 5                            Arrest increased offense      
                                                          frequency at 12 mos           

Dunford 1990                 5                            Arrest warrant reduced        
                                                          absent offender recidivism    

Sherman et al 1991           5                            Arrest had no effect on       
                                                          recidivism at 6 mos; short    
                                                          arrest increased recidivism   
                                                          after 12 mos                  

Sherman et al 1992                                                                      
     (Milwaukee)             4                            Arrest deters employed,       
                                                          criminogenic for unemployed   
     (Omaha)                 4                            Same as preceding             

Berk et al 1992a             5                            Arrest reduced recidivism     

Berk et al 1992b             4                            Arrest deters employed, not   

Pate et al 1991              5                            Arrest reduced recidivism     

Pate and Hamilton 1992       5                            Arrest deters employed,       
                                                          criminogenic for unemployed   

Hirschel et al 1992          5                            Arrest increases official     

Marciniak 1994               4                            Arrest deters in areas of     
                                                          high employment & marriage;   
                                                          increases recidivism in       
                                                          areas of low employment &     

The consistent individual level evidence of the criminogenic effects of arrests for juveniles is all longitudinal, but only one of the studies is a randomized experiment (Klein, 1986). The other studies are natural observations of the difference in self-reported offending before and after juvenile offenders were arrested. These studies cannot adequately control for the rival hypothesis that the same factors that led to the youth being arrested also caused a higher level of repeat offending. A pattern of "defiance" (Sherman, 1993), for example, would account for both variables and their correlation. The Klein (1986) experiment reported some difficulties in maintaining random assignment, but still managed to make the formal charging of juveniles in police custody a matter of equal likelihood across cases. Holding juvenile characteristics relatively constant, then, Klein found that the more legalistic the processing of a juvenile suspect, the higher the official recidivism rate.2 In interpreting these results, it is necessary to recall that most juvenile offenses are for fairly minor offenses, and that most juveniles with one police contact never have another (Wolfgang, Figlio and Sellin, 1972). Thus to a certain degree, arresting some juveniles and not others for such offenses may be perceived as arbitrary or procedurally unfair.

The evidence on the effects of arrest for misdemeanor domestic violence is contradictory across cities but consistent within arrestee characteristics. While three experiments have found some evidence of deterrent effects of arrest (Sherman and Berk, 1984; Pate, Annan and Hamilton, 1991; Berk et al, 1992), three other experiments have found some evidence that arrest increases the frequency of officially detected offending (Sherman, et al, 1991; Hirschel et al, 1992; Dunford, 1992). All four of these six experiments for which the data have been analyzed separately by employment status of the offender show consistent results. Arrest increases repeat offending among unemployed suspects while reducing it among employed suspects. Marciniak (1994) has shown that this difference operates even more powerfully at the census tract level than at the individual level, with arrest backfiring irrespective of individual employment status in neighborhoods of concentrated unemployment and single parent households. There is a literature raising concerns about measurement issues in these data (Garner and Fagan, 1995; Fagan, 1996) that are not generally raised about other studies in the police literature. Yet there is no other example in the police literature of six similar randomized experiments all testing similar hypotheses with similar (though not identical) designs, and these studies feature a scientific rigor score that is twice the mean of all studies classified for this chapter. The consistency of the effects of arrest on crime for employed and unemployed offenders even extends to similarity in effect sizes.

6. Proactive Arrests

Like the evidence on focused patrol, the evidence on the focused proactive arrest hypothesis is generally supportive across a wide range of studies and research designs. While most of the studies are relatively modest in scientific strength, there are some randomized controlled experiments. With the exception of arrests targeted on drug problems, there appear to be substantial results from focusing scarce arrest resources on high risk people, places, offenses and times.

The evidence on high-risk people comes from two strong ( level 4) evaluations of police units aimed at repeat offenders. The Washington, D.C. unit employed pre-arrest investigations, designed to catch offenders in the act of crime to enhance the strength of evidence. The Phoenix police unit employed post-arrest investigations, designed to enhance the evidence in the offenders latest case based upon the length and nature of the offender's prior record. Both projects aimed at increasing the incarceration rate of the targeted offenders, and both succeeded. Just how serious or active the offenders were is an important issue in these studies, one which could illuminate future analyses of dollars invested per crime prevented.

Two weaker studies use national samples of cities to test the effects of police arrest rates for minor offenses on robbery. Both employ multivariate models to control for the effects of some of the other factors that could influence the city's robbery rate. Both find that the higher the per capita rates of traffic arrest, the lower the rates of robbery. One uncontrolled factor in these analyses is the number of pedestrian robbery opportunities. This may be much higher in cities where there is less use of automobiles, such as New York City, in which under 3% of the US population suffers 12% of the reported robberies. Since that is the only crime type for which New York is so disproportionate, and since other dense, pedestrian cities like Baltimore and Boston also have high robbery rates, there may be a spurious relationship between traffic enforcement and robbery. That is, the more cars per capita, the fewer robbery opportunities and the more traffic enforcement opportunities.

Table 8-6: Proactive Arrests.

The higher the arrest rate for high-risk offenders and offenses, the lower the rates of serious violent crime.3

8-6.a. Repeat Offenders.

Studies                      Scientific Methods Score     Findings                      

Martin and Sherman 1986      4                            Targeted offenders more       
                                                          likely to be arrested and     
                                                          incarcerated (Washington)     

Abrahamse et al 1991         4                            Post-arrest case enhancement  
                                                          increases odds of arrestees   
                                                          being incarcerated (Phoenix)  

Table 8-6.b. Traffic and disorderly conduct arrests

Studies                      Scientific Methods Score     Findings                      

Wilson and Boland 1978       2                            Cities with higher arrest     
                                                          rates have less crime         

Sampson and Cohen 1988       2                            Same as preceding             

Weiss and McGarrell 1996     3                            Increased traffic tickets,    
                                                          reduced robbery               

Table 8-6.c. Drug market areas

Studies                      Scientific Methods Score     Findings                      

Kleiman 1988 (Lynn)          2                            Crackdown on heroin market,   
                                                          violence down                 

Kleiman 1988 (Lawrence)      2                            Crackdown on heroin market,   
                                                          violence up                   

Zimmer 1990 and Kleiman      2                            Crackdown on heroin market,   
    1988 (NYC)                                            violence down                 

Sviridoff et al 1992         3                            Crackdown on crack market,    
                                                          violence flat                 

Uchida et al 1992            3                            Inconsistent changes in       
(Birmingham)                                              violence after arrests up     

Uchida et al 1992 (Oakland)  3                            Buy & bust plus               
                                                          door-to-door, robbery down    
                                                          Each strategy alone, no       

Sherman and Rogan 1995       5                            Raids of crack houses         
                                                          reduced crime for 12 days     

Weisburd and Green 1995      4                            Crackdowns on hot spots       
                                                          reduced disorder; no effects  
                                                          on violence or property       

Annan and Skogan 1993        3                            Drug crackdown in public      
                                                          housing, no effect on crime   

Table 8-6.d. Drunk driving

Studies                      Scientific Methods Score     Findings                      

Ross 1981 review:                                         Arrests up sharply, drop in   
     Ross 1973 (U.K.)        2                            crashes decays over time      
     Ross 1975               2                            Same as preceding             
                             2                            Same as preceding             
     Ross 1977 (Chesire 1)                                                              
                             2                            Same as preceding             
     Ross 1977 (Chesire 2)                                                              
                             2                            Same as preceding             
     Hurst-Wright 1980                                                                  
(NZ1)                        2                            Same as preceding             
     Hurst-Wright 1980       2                            Same as preceding             
     Ross et al 1982                                                                    

Homel 1993                   3                            Increased state arrest rate   
                                                          reduced deaths over 10        
                                                          years, but not in comparable  

Table 8-6.e. Zero Tolerance Arrests

Studies                      Scientific Methods Score     Findings                      

Boydstun 1975; Sherman 1990  3                            More field interrogations,    
                                                          fewer outdoors crimes         

Reiss 1985                   3                            More police regulation of     
                                                          conduct, fewer "soft" crimes  

Pate et al 1985; Skogan      3                            Same as preceding             

Sherman 1990                 2                            Disorder crackdown, no        
                                                          robbery reduction             

Kelling and Coles 1996       2                            Fare-beating, crackdown,      
                                                          robbery reduction in subways  

That is just the kind of limitation in causal inference that experiments can address. Quasi-experimental evidence on this hypothesis was recently reported by the Hudson Institute study of the Indianapolis Police Department, in which substantial increases in traffic enforcement in a high robbery area were followed by a sharp reduction in robbery (Weiss and McGarrell, 1996).

The evidence on drug crackdowns shows no consistent reductions in violent crime during or after the crackdown is in effect. The strongest evidence is the randomized experiment in raids of crack houses (Sherman and Rogan, 1995), in which crime on the block dropped sharply after a raid. The rapid decay of the deterrent effect in only seven days, however, greatly reduces the cost-effectiveness of the labor-intensive raid strategy. Only the high yield of guns seized per officer-hour invested (Shaw, 1994) and its possible connection to community gun violence over a longer time period (Sherman, Shaw and Rogan, 1995) showed great cost-effectiveness. Other drug enforcement strategies in open-air markets have even less encouraging results, with the exception of the Jersey City experiment in which the principal outcome measure was disorder, not violence.

The evidence on drunk driving, in contrast, is one of the great success stories of world policing. Despite relatively low rigor scores, the sheer numbers of consistent results from quasi-experimental evaluations of proactive drunk driving arrest crackdowns suggest a clear cause and effect. The ability of the police to control drunk driving appears to be a direct and linear function of the amount of effort they put into it (Homel, 1990). Since more deaths are caused annually by drunk driving than by homicide, the cost effectiveness of saving lives through DUI enforcement may well be far greater than for homicide prevention. The evidence on drunk driving prevention sees far clearer than anything we know how to do to have police prevent murders.

The evidence for the broken windows-zero tolerance arrests hypothesis (Wilson and Kelling, 1982) is also consistently supportive. The research designs are only moderately strong, but they all suggest that a police focus on street activity can help reduce serious crime. The specific tactics by which this is accomplished can be controversial, and some methods used in the 1982 Newark test have been described in the literature as "unconstitutional" (Skolnick and Bayley, 1985:199), including the ordering of loitering teenage males off of street corners on the grounds of obstructing traffic. Field interrogations have often been a flash point of poor police-community relations, yet they have also been a favorite crime prevention tactic for police in both the US and Europe. The evidence from both the San Diego field interrogation experiment (Boydstun, 1975) and the NIJ Oakland city center study (Reiss, 1985) suggest that it is possible to regulate public behavior in a polite manner that fosters rather than hinders police legitimacy. That possibility, however, is by no means guaranteed, and generally takes substantial managerial investment in order to bring about.

The larger concern about zero tolerance is its long-term effect on people arrested for minor offenses. Even while massive arrest increases, such as those in New York City, may reduce violence in the short run--especially gun violence--they may also increase serious crime in the long run. The negative effects of an arrest record on labor market participation are substantial (Schwartz and Skolnick, 1963; Bushway, 1996). The effects of an arrest experience over a minor offense may permanently lower police legitimacy, both for the arrested person and their social network of family and friends. The criminogenic effect of arrest may make arrestees more defiant (Sherman, 1993) and more prone to anger in domestic violence and child abuse. The data suggest that zero tolerance programs should be evaluated in relation to long-term effects on those arrested, as well as short-term effects on community crime rates. Program development to foster greater legitimacy in the course of making the arrests is also advisable, based on findings from procedural justice research (see hypothesis 7.d below). This could include, for example, a program to give arrested minor offenders an opportunity to meet with a police supervisor who would explain the program to them, answer questions about why they are being arrested, and give them a chance to express their views about the program while listening respectfully to them. Such innovations would not be expensive, but would also pose many testable hypotheses.

7. Community Policing

The results of available tests of the community policing hypotheses are mixed. The evidence against the effectiveness of police organizing communities into neighborhood watches is consistent and relatively strong. The evidence about the crime prevention benefits of more information flowing from citizens to police is at best only promising. The two tests of police sending more information to citizens are both very strong, but clearly falsify the hypothesis. The tests of increasing police legitimacy are the most promising, especially since they draw on a powerful theoretical perspective that is gaining growing empirical support.

One of the most consistent findings in the literature is also the least well-known to policymakers and the public. The oldest and best-known community policing program, Neighborhood Watch, is ineffective at preventing crime. That conclusion is supported by moderately strong evidence, including a randomized experiment in Minneapolis that tried to organize block watch programs with and without police participation in areas that had not requested assistance (Pate et al, 1987). The primary problem found by the evaluations is that the areas with highest crime rates are the most reluctant to organize (Hope, 1995). Many people refuse to host or attend community meetings, in part because they distrust their neighbors. Middle class areas, in which trust is higher, generally have little crime to begin with, making measurable effects on crime almost impossible to achieve. The program cannot even be justified on the basis of reducing middle class fear of crime and flight from the city, since no such effects have been found. Rather, Skogan (1990) finds evidence that Neighborhood Watch increases fear of crime.

Another popular program for increasing contact between police and public is community meetings. The careful NIJ evaluation of the Madison, Wisconsin community policing project in which meetings played a central role found no reduction in crime (Wycoff and Skogan, 1993). A different approach to the meetings in Chicago shows more promise, with the meetings focused much more precisely on specific crime patterns in the area and ideas for what the police should do to attack those problems. While the crime reduction evidence for "community policing, Chicago style" is mixed, it is striking that Chicago has mobilized high crime communities to participate in these meetings (Skogan, 1996). Unlike neighborhood watch meetings, the Chicago meetings are held in public places rather than local residences. The best attendance at these meetings for almost two years has been found in the police districts with the highest crime rates.

A less popular but often effective community policing practice is door to door visits by police to residences during the daytime. These visits may be used to seek information, such as who is carrying guns on the street (Sherman, Shaw and Rogan, 1995). The visits may be used to give out information, such as burglary reduction tips (Laycock, 1991). The visits may be used simply to introduce local police officers to local residents, to make policing more personal (Wycoff et al, 1985). Four out of six available tests of the door to door visits show modestly strong (rigor = 3) evidence of substantial crime prevention. In the NIJ-funded Houston test, for example, the overall prevalence of household victimization dropped in the target area substantially, with no reduction in the comparison area. The prevention effects were primarily for car-breakins and other minor property crime. Here again, however, there was a substantial "Matthew effect" (see Chapter 1): the benefits of the program were highly concentrated among white middle class homeowners, with virtually no benefit for the Asian, Hispanic and African-American minorities living in rental housing in the target area (Skogan, 1990).

A far more popular program is far less effective. Police storefronts are often requested by communities, often staffed during business hours by a mix of sworn police, paid civilians and unpaid volunteers. The evidence from tests of substations in Houston, Newark and Birmingham

(continued after Tables)

Table 8-7: Community Policing

Increasing the quantity and quality of police-citizen contact reduces crime. Tests of this basic hypothesis omitting measurement of an intervening causal mechanism have been done:

Table 8-7.a. Neighborhood Watch

Studies                      Scientific Methods Score     Findings                      

Lindsay and McGillis 1986    3                            Burglary reduced for 18 mos   

Pate et al 1987;             4                            No effect of block watch on   
     Skogan 1990                                          Poorer areas had less         

Rosenbaum 1986               3                            Same as preceding             

Bennett 1990                 3                            Same as preceding             

Table 8-7.b. Intelligence from citizens to police.

Studies                      Scientific Methods Score     Findings                      

Community Meetings                                                                      

Wycoff and Skogan 1993       3                            No drop in victimization      
                                                          after increase in             
                                                          police-community meetings in  
                                                          target district               

Skogan et al 1995            3                            After 18 monthly              
                                                          police-community meetings in  
                                                          each beat in 5 districts,     
                                                          reductions in some crimes     
                                                          and victimization measures    
                                                          but not others                

Door-to-Door Contacts                                                                   

Wycoff et al 1985; Skogan    3                            Door-to-door police visits;   
       1990                                               victimization dropped         

Pate et al 1985; Skogan      3                            Door-to-door visits &         
1990                                                      storefront, crime dropped     

Laycock 1991                 3                            Door-to-door visits,          
                                                          burglary down by ___%         

Sherman et al 1995           3                            Door-to-door visits, no drop  
                                                          in crime                      

Uchida et al 1992            3                            Visits plus Buy and Bust,     
                                                          crime down                    

Uchida et al 1992            3                            Visits alone, no crime        


Wycoff and Skogan 1986       3                            Storefront open, no drop in   

Uchida et al 1992            3                            Storefront open, no           
                                                          difference in crime           

Pate et al 1985; Skogan      3                            (See above under              
     1990                                                 "door-to-door")               

Table 8-7.c. Increasing the flow of information from police to citizens.

Studies                      Scientific Methods Score     Findings                      

Pate et al (Newark)          5                            Monthly newsletter with       
                                                          crime data failed to reduce   
                                                          victimizations of recipients  

Pate et al (Houston)         5                            Same as preceding             

Table 8-7.d. Legitimacy

Studies                      Scientific Methods Score     Findings                      

Skogan 1990 (Houston)        3                            Doorknock visits reduced      
                                                          fear of police, reduced       

Tyler 1990                   1                            Definition of past police     
                                                          treatment as fair increases   
                                                          expected obedience to law in  
                                                          the future                    

Paternoster et al 1996       2                            Definition of treatment at    
                                                          arrest as fair, lower         
                                                          recidivism in domestic        

Skogan et al 1995            3                            Perceived increased           
                                                          responsiveness of police to   
                                                          community in 4 districts,     
                                                          perceived reduction in        
                                                          serious crime in 3 of those   

(AL) consistently shows no impact on crime. While there are some positive citizen evaluations associated with storefronts, the problems of staffing the offices once they are open may counterbalance any non-crime benefits.

Increasing the flow of information from police to public has been tested in the form of police newsletters. In two randomized NIJ-funded experiments, the Newark and Houston police departments found no effect of newsletters on the victimization rates of the households receiving them. The finding was true for both newsletters with and without specific data on recent crimes in the community.

The most promising approach to community policing is also the most theoretically coherent. Based on two decades of laboratory and field studies on the social psychology of "procedural justice," a growing body of research suggests that police legitimacy prevents crime. Tyler (1990) finds a strong correlation across a large sample of Chicago citizens between perceived legitimacy of police and willingness to obey the law. The legitimacy was measured by citizen evaluations of how police treated them in previous encounters. This finding is consistent with the Houston door-to-door experiment, in which citizen fear of police after a major scandal over police beating to death a Mexican immigrant was reduced by the door-to-door visits. Community policing Chicago style (Skogan, et al 1996) also find the greatest perceived reduction in serious crime in the districts where surveys showed police were "most responsive" to citizen concerns. The most powerful test of this hypothesis is the Paternoster et al (1996) reanalysis of the Milwaukee Domestic Violence Experiment, which found that repeat domestic violence was lowest among arrestees who thought police had treated them respectfully; a powerful effect on recidivism was associated with police simply taking the time to listen to the offender's side of the story. The capacity of police legitimacy to prevent crime is something community policing may well be effective at creating; Skogan's (1994: 176) review of six community policing evaluations (SM scores = 2 or 3) found every one showed positive or improved perceptions of police in the treated areas.

Still in progress, but with encouraging preliminary results, is the Australian test of community accountability conferences. The Australian Federal Police in the Australian capital, Canberra, use this procedure as an alternative to prosecuting juveniles. Only cases in which the offender(s) admit(s) guilt and the victim(s) are willing to attend the conference are eligible. The conference of offenders and victims with their respective families and friends is led by a trained police officer, who focuses the discussion on what happened, what harm it caused, and how the harm can be repaired. The officer tries to insure that everyone, especially victims, is allowed to have their say. Sometimes offenders apologize, but always an agreement for repaying the cost of the crime to the victim is reached; failure to do so results in the case being prosecuted. Preliminary findings from subsequent interviews with victims and offenders in a randomized experiment show that the procedure greatly increases respect for police and a perception of justice, regardless of the outcomes (Strang, 1996; Barnes, 1996). The National Institute of Justice has funded a similar ongoing project in Bethlehem, Pennsylvania. This method may turn out to have long-term effects on police legitimacy in the eyes of both juvenile offenders and their families, which could in turn reduce crime.

The interesting point about the Australian model of community policing, as noted in Chapter 2, is that it builds on actual community ties rather than anonymous geographic areas. Moreover, the attendees form a community of concern about the criminal act bringing them together, holding the offender accountable for over an hour to a "village-like" community rather than for a few minutes to a distant and anonymous judge. Of all the approaches to community policing yet tried, this one may have the most focused empowerment of "community" to prevent future crimes.

8. Problem-Oriented Policing

The tests of this hypothesis are generally more positive than the tests of community policing. As Moore (1992) suggests, however, this may be due to a process of selective reporting, in which failures are not included. The most basic problem with testing this very rich and complex hypothesis is that it is essentially about insight, imagination and creativity. The essence of problem-oriented policing as Goldstein (1979) defined it is science itself (Sherman and Strang, 1996): classification, prediction, and causation. Evaluations of the scientific method, paradoxically, are not readily susceptible to the scientific method--except in gross comparison to unscientific methods. From this perspective, problem-oriented policing embraces all of the other strategies described in this chapter, with the problem to be solved that of crime prevention.

This section reviews some evidence on police efforts to prevent crime that do not fall into the preceding seven hypotheses, and that self-consciously adopted a scientific process that involved police officers in analyzing crime patterns, imagining and creating an intervention, and testing it in the field. The two basic categories of interventions reported in the literature to date are "removing criminogenic substances" and "separating potential victims and offenders." These two categories simply reflect a convergence of police and criminological thinking about the proximate causes of criminal events. There is nothing in the basic problem-oriented policing (POP) strategy (Goldstein, 1979) that requires the use of these two approaches. Many others are possible, and may even be more effective. If POP succeeds at making scientific research and development the core technology of police work (Reiss, 1992), we may expect that its approaches to crime prevention will evolve with the evolution of knowledge about crime causation.

8.a. Criminogenic Substances. The evidence on cash control is weak but suggestive. As part of a multiple intervention strategy to reduce crime in an English public housing project, the coin-operated gas heaters were removed from residences. Rather than having the cash in the house as an attraction to burglars, the gas charges were switched to monthly billing. Burglary went down substantially. It is uncertain, however, whether other efforts, such as the "cocoon" neighborhood watch around recently burglarized residences, might account for the crime reduction.

The evidence on gun carrying is stronger. In the NIJ Kansas City Gun Experiment, police focused traffic enforcement and field interrogations on gun crime hot spots during hot times (Sherman, Shaw and Rogan, 1995). With special training in the detection of carrying concealed weapons, police focused on seizing illegally carried weapons. Gun seizures in the target area rose by 60%, and gun crimes dropped by 49%. A similar area in a different part of town showed no change in either guns seized or gun crimes. In Boston, police have used a mix of strategies to discourage gun carrying in public places among juveniles, especially gang members and probationers. Qualitative evidence from an NIJ project suggests gun carrying by the high-risk groups has been substantially reduced, while early quantitative evidence shows an elimination of juvenile gun homicide (Kennedy et al 1996).

The evidence on alcohol and prostitution is also encouraging, and was presented in Chapter Seven in the discussions of taverns, bars, traffic barriers and street closures.

In the Minneapolis RECAP (REpeat Call Address Policing) experiment, however, four police officers were unable to implement a broad mix of efforts to separate potential victims and offenders across a sample of 250 target addresses. The YMCA refused to limit access to its lobby during evening hours, the Public Library refused to bar intoxicated persons, public housing officials were unable to segregate young "disabled" but predatory alcoholics from elderly co-residents, and private landlords resisted efforts to evict drug dealers (Sherman, 1990; Buerger, 1994). While a randomized experimental design gave the test strong science, police inexperience at persuading property managers gave the strategy a weak technology. Given the theoretical power of the idea, further development of the methods of persuasion might be justified, and only then followed by further research.

One of the most popular practices for separating victims and offenders is evening curfews for juveniles. While such curfews give police additional powers to search for guns, they have not been used consistently in that fashion. The primary objective is to get kids, not guns, off the streets. Some cities, such as San Antonio, have reported reductions in reported crimes against juveniles. But in preliminary results of an NIJ evaluation, Adams (1996) finds no consistent crime reduction effects across cities adopting curfews. The scientific rigor of these studies is quite low given their complete absence of control groups, and there may also be difficulties in police willingness to follow curfew policies. Thus the question of the effectiveness of curfews at preventing youth violence is still quite open to further research and development.

Table 8-8: Problem-Oriented Policing

The more accurately police can identify and minimize proximate causes of specific patterns of crime, the less crime there will be.

Table 8-8.a. Reducing Gun Carrying in Public. The more police can remove guns from public places or deter people from carrying them in the micro-environments of criminal events, the fewer crimes there will be.

Studies                      Scientific Methods Score     Findings                      

Sherman et al 1995           3                            Increased gun seizures,       
                                                          reduced gun crimes            

Kennedy et al 1996           2                            Reduced gun carrying, fewer   
                                                          gun crimes                    

Table 8-8.b. Separating Potential Victims and Offenders. The more police can reduce the intersection of motivated offenders in time and space with suitable targets of crime, the less crime there will be.

Studies                      Scientific Methods Score     Findings                      

Sherman 1990; Buerger 1994   5                            Unable to get landlords to    
                                                          restrict offender access      

Adams 1996                   2                            Youth curfews, no consistent  
                                                          reduction in crime.           


For all of its scientific limitations, the evidence shows substantial consistency on a number of the hypotheses, and some tentative conclusions on others. All science, of course, is provisional, with better research designs or theories revealing previously undiscovered patterns. It is no small achievement that police crime prevention research has developed to the point of having reached some conclusions to discard.

The available evidence supports two major conclusions about policing for crime prevention. One is that the effects of police on crime are complex, and often surprising. The other is that the more focused the police strategy, the more likely it is to prevent crime. The first conclusion follows from the findings that arrests can sometimes increase crime, that traffic enforcement may reduce robbery and gun crime, that the optimal deterrent effect of a police patrol may be produced by 15 minutes of presence in a hot spot, and that prevention effects generally fade over time without modification and renewal of police practices. The second conclusion follows from the likely failure to achieve crime prevention merely by adding more police or shortening response time across the board.

The substantial array of police strategies and tactics for crime prevention (Reiss, 1995) has a small but growing evaluation literature. Using the standard of at least two consistent findings from level 3 scientific methods score (well-measured, before-after studies with a comparison group) and a preponderance of the other evidence in support of the same conclusion, the research shows several practices to be supported by strong evidence of effectiveness, and several with strong evidence of ineffectiveness.

What works:

o increased directed patrols in street-corner hot spots of crime

o proactive arrests of serious repeat offenders

o proactive drunk driving arrests

o arrests of employed suspects for domestic assault

What doesn't:

o neighborhood block watch

o arrests of some juveniles for minor offenses

o arrests of unemployed suspects for domestic assault

o drug market arrests

o community policing with no clear crime-risk factor focus

Several other strategies fail to meet the test of strong evidence for generalizable effectiveness, but merit much more research and development because of encouraging findings in the initial research.

What's Promising:

o police traffic enforcement patrols against illegally carried handguns

o community policing with community participation in priority setting

o community policing focused on improving police legitimacy

o zero tolerance of disorder, if legitimacy issues can be addressed

o problem-oriented policing generally

o adding extra police to cities, regardless of assignments

o warrants for arrest of suspect absent when police respond to domestic violence

What is notably absent from these findings, however, are many topics of great concern to police. Gang prevention, for example, is a matter about which we could not find a single impact evaluation of police practices. Police curfews and truancy programs lack rigorous tests. Police recreation activities with juveniles, such as Police Athletic Leagues, also remain unevaluated. Automated identification systems, in-car computer terminals, and a host of other new technologies costing billions of dollars remain unevaluated for their impact on crime prevention. There is clearly a great deal of room for further testing of hypotheses not listed here due to the absence of available scientific evidence.

These conclusions suggest important implications for both DOJ crime prevention funding of police agencies, and improving that effectiveness through stronger evaluations.

The Effectiveness of DOJ Programs

Local police agencies receive crime prevention funding from a wide range of DOJ programs (see Chapter One). The evidence cited in this chapter indicates that most of the funding supports programs shown to be effective. There is also evidence that Congress could increase the effectiveness of the funding with modifications to several formula grant allocation criteria. The two largest components (multijurisdictional task forces and police equipment) of the two largest OJP programs (estimated $361 million total in FY 1996 funding) are of unknown effectiveness, suggesting a high priority for evaluation research. Also of unknown effectiveness are the Violence Against Women grants for police. Byrne grants in the drug enforcement purpose area supporting unfocused proactive arrest programs in drug market areas appear from the available evidence to be ineffective at preventing crime.

How Police Funds Are Allocated. The largest single funding source is the Office of Community-Oriented Policing Services (COPS), which distributes funding for the 100,000 planned extra police officers irrespective of crime rate and partially on the basis of population served by each police agency; the major constraint is that half of all funds must go evenly to police agencies serving over 150,000 people. Other DOJ funds for police are distributed through the Office of Justice Programs (OJP) and its constituent offices.

Figure 8-2

Federal Funding Programs for Local Police

DOJ Office and Program       Purpose Areas                Total Funding (in bold)       

COPS Office                  Cops on the beat             $1.4 Billion                  

Office of Justice Programs                                                              

Bureau of Justice            Law Enforcement Equipment    $171 million                  
Assistance                   Law Enforcement Hiring         65 million                  
    Local Law Enforcement    Law Enforcement Overtime       51 million                  
      Block Grants           Total                        $287 million                  

Bureau of Justice            Multijurisdictional Task                                   
Assistance                                 Forces         $190 million                  
    Byrne Memorial Grants4    against drugs                  26 million                  
                             Urban Enforcement vs. drugs                                
                             Law Enforcement                15 million                  
                                          Effectiveness      3 million                  
                             Organized Crime              $234 million                  

Violence Against Women                                                                  
   Grant Office                                                                         
    Encourage Arrests                                                                   
         Program             Total                        $46 Million                   

Violence Against Women                                                                  
   Grant Office              Law Enforcement                                            
    STOP Block Grants        Total                        $30 Million                   

OJJDP Community Policing                                                                
      for Juveniles          Total                        $16 million                   

Other Programs, amounts                                                                 
n.a.: Weed and Seed,                                                                    
OJJDP Serious Chronic                                                                   
Violent and Anti-Gang, BJA                                                              
Comprehensive Communities                                                               
Program, others                                                                         

Total of Major Funding                                                                  
Programs                                                  $2.013 Billion                

Because each OJP grant award may be allocated among a variety of local agencies including police, there is no exact count of how much federal funding goes to police agencies. Purpose areas within the major funding programs, however, provide a good approximation (See Figure 8-1). While simply summing the purpose area allocations may overestimate police agency funding as distinct from other "enforcement" agencies, such as prosecutors, the difference is probably more than made up by other programs for which we have no precise estimates.

The largest OJP source of local police funding is apparently the Local Law Enforcement Block Grants Program, which distributes formula grants to units of local government on the basis of both state and local Part I violent crimes for the preceding three years; 71 percent of the $405 million ($287 million) in 1996 formula funds were allocated to Purpose Areas specifically directed to law enforcement, and more may have been awarded through other purpose areas. At similar levels of funding are the $475 million in 1996 formula funds provided as Byrne Grants on the basis of population, of which 50% ($237 million at 1996 funding levels) were allocated to Purpose areas specifically directed to law enforcement in 1989-94 (Dunworth, et al, 1997). The Violence Against Women Act includes two major funding mechanisms for local policing, the $120 STOP Violence Against Women Formula Grants (of which 25%, or $30 million in FY 1996, must be allocated to improving law enforcement) and the competitive Grants To Encourage Arrest Policies ($46 million in 1996). There are also funds for community policing components appropriated through Weed and Seed, BJA's Comprehensive Communities Program (CCP), and these OJJDP Programs: Kids and Guns, the Comprehensive Community-Wide Gang Prevention, Intervention and Suppression Program, the Comprehensive Strategy for Serious, Violent and Chronic Offenders, and Juvenile and Child-Centered Community-Oriented Policing. Many other smaller funding programs support local police crime prevention programs. The current estimated total is in excess of $2 billion per year.

Implications of Available Science. The DOJ funding programs support a wide range of local police activity. Some types of police activity DOJ supports have no impact evaluations, while others can be evaluated directly or indirectly with the evidence reviewed in this chapter. Much of the funding simply supports additional police presence regardless of the activities police undertake. Given the promising evidence on the effectiveness of simply adding police officers to police agencies, the scientific review suggests that these funding programs may be effective. It also suggests, however, that the funding programs could be even more effective if the statutory formula were changed.

In general, the evidence suggests that federal appropriations to prevent crime through additional policing is most effective when allocated on the basis of serious crime rather than on the basis of population size. This implication is drawn from several scientific conclusions. One is the "promising" finding that across all large cities, more police produced less serious crime. A second is the finding that each additional police officer assigned to a big city prevents six times as many serious crimes each year as an officer assigned nationally by population (Marvell and Moody, 1996). A third conclusion is the finding that directed patrol in crime hot spots "works" to prevent crime in those hot spots, the greatest micro-level concentrations of crime. A fourth conclusion is the "promising" finding that police can reduce gun crime by intensified enforcement of the laws against carrying concealed weapons. This finding suggests that federally funded police work in hot spots of gun crime could have a substantial impact on the national homicide rate, just as police may have done in New York City (Reppetto, 1996). Taken together, these findings suggest that the Congress could consider revising the statutory allocation formula based not only on city-level violent crime, but beat-level and block level crime as well. Such a revision would be more effective in directing federal funds as precisely as possible for maximum crime prevention.

Refining a Crime-Based Grant Formula. If the Congress did decide to move towards more crime-based grant formulas for allocating police funding, it would be worth considering more precise criteria. The LLEBG formula based on total Part I violent crimes is problematic for several reasons. One is that police agencies vary in how they report the largest single category of Part I violence, aggravated assault. The boundary between aggravated and simple assaults is marked very differently in different cities. In Milwaukee in the early 1990s, for example, when someone pointed a gun at another person and threatens to shoot, the offense is classified as an aggravated assault. In many other police agencies, that conduct might not even result in an offense report being taken, or at most a simple assault report would be filed; this merely reflects different local traditions in defining "attacks" and "attempts" (the latter of which the FBI asks police to count as completed crimes) for Uniform Crime Reporting Purposes. Differences in aggravated assault rates thus do not reflect the level of serious violence as reliably as differences in homicide rates. But aggravated assault counts clearly determine the allocation of LLEBG money; they constituted sixty-one percent of all Part I violence in 1995, while homicides constituted only one percent.

Taking aggravated assaults out of a crime-based formula raises other issues. Homicide alone is a more consistently reported but more unstable indicator, vary widely in many cities from year to year, which would create instability in funding levels if used to allocate funding. Robberies are much more numerous, and more consistently reported than aggravated assault and rape. On balance, the Congress may find a combination of robbery and homicide counts to be the most reliable indicator of the greatest need for supplementary police presence. The same is true for possible statutory requirements on how federal funds should be spent on policing within cities, with hot spots of robbery and homicide receiving top priority. The concentrations of those crimes in the "hot times" of 7 pm to 3 am is a further element a refined crime-based formula for allocating police funding could consider.

COPS Program. The procedure for distributing COPS funds by jurisdiction is the major implication of the scientific review for the COPS Program. Another important issue, however, is the purposes for which COPS officers are funded. While there is promising evidence that any increase in police officers is helpful, there is even stronger evidence of crime prevention effects of specific activities. While COPS Program language has stressed a community policing approach, there is no evidence that community policing per se reduces crime without a clear focus on a crime risk factor objective. There is strong evidence, however, that directed patrols and programs targeted on criminogenic substances like guns and alcohol can be effective in attacking crime hot spots. The evidence on crime prevention in places reviewed in Chapter Seven also finds promising support for problem-oriented policing, which could be another more tightly defined purpose area for supplementary police. Thus while the scientific evidence indicates the COPS program is effective, it also suggests it could be more effective if its funding was more focused upon police programs of proven effectiveness.

Local Law Enforcement Block Grants (LLEBG). The scientific evidence also suggests that most of the wide range of police activities supported by the LLEBG program are effective in preventing crime. The major exception is for law enforcement equipment and technology, which received 60 percent of 1996 appropriations directed to specifically to police (see bar graphs). As noted above, there are no published impact evaluations of the effects of equipment and technology on crime. Thus the effectiveness of this funding is unknown. Impact evaluations of this activity are certainly feasible, and could result in substantial improvements in the uses of such technologies as firearms identification, automated fingerprint identification systems, and in-car computer search capacity for stolen cars and arrest warrants. While the common sense value of such systems may appear substantial, the prior history of other equipment items suggests that there is much to be learned from careful analysis of its ultimate effects upon crime, and not just intermediate indicators like arrests.

The Congress could also consider refining the crime-based formula for LLEBG as described above, especially for the usage of police overtime. Many police agencies are now using such overtime to mount directed patrols of the kind found effective in this Chapter. The statutory plan could better insure that overtime is used in the most effective ways possible by incorporating the "hot times, hot spots" criteria, or other programs of proven effectiveness, for overtime work. It could offer additional special purpose areas, such as repeat offender units, which have also been found effective in apprehending and incarcerating serious violent felons.

Byrne Grants. The many uses of Byrne grants almost certainly include the programs of proven effectiveness identified in this Chapter. The most heavily funded Purpose Area, however, is of unknown effectiveness. Multijurisdictional Task Forces against drugs received 40 percent of Byrne Formula funding in the years 1989-94 (Dunworth, et al, 1997), but they have never been subjected to a published impact evaluation. To the extent that the Byrne Program was intended to apprehend drug dealers, it may be inappropriate to consider these task forces a prevention program. It does not seem inappropriate, however, to specify measurable goals for the program, and to design an impact evaluation to test the effectiveness of the Task Forces in accomplishing those goals.

A Purpose area for Byrne Grants in which evaluation research indicates ineffective use of funding is "urban enforcement" against drugs, estimated at $26 million in FY 1996. To the extent that these grants support street-level drug enforcement with an emphasis on arrests or drug raids, the money is unlikely to prevent crime. The conclusions of multiple evaluations show that such practices do not reduce violent crime or disorder in the absence of constant police presence, and sometimes not even then.

New purpose areas under the Byrne Grants include both drunk driving and gang enforcement and prevention. The scientific evidence strongly supports the use of Byrne grants for drunk driving enforcement as likely to prevent many deaths and serious injuries. It may also have the prevention effect of reducing gun crime, since so many illegally carried guns and gun criminals wanted on warrants can be removed from the streets through traffic enforcement. There is also a preponderance of available evidence that traffic enforcement that can help reduce robbery. There are no impact evaluations available on the effectiveness of police strategies against gangs.

STOP Violence Against Women Block Grants. A review of the detailed listing of FY 1995 STOP grants for law enforcement shows that they generally supported activities of unknown effectiveness. Programs such as training police about domestic violence, hiring domestic violence specialists in police agencies, and computer software for domestic violence records all appear to be useful at face value, but have not been subject to published evaluations. While the individual grant awards are small, there are many in the same program categories. An evaluation program addressing the effectiveness of the major funding categories could enhance the currently unknown effectiveness of most of these grants.

Grants to Encourage Arrest Policies. These grants apparently support similar activities as the STOP grants, although with a more narrow focus on domestic violence against women. To the extent that these grants result in more arrests in areas of high employment, the scientific evidence suggests they will be effective in reducing domestic violence against women. There is also strong scientific evidence, however, that under certain conditions arrests substantially increase future domestic violence against women. This research raises a critical need for further rigorous research, development and program evaluation, which would attempt to discover means to overcome the apparent criminogenic effects of arrest on certain batterers. This research program, much of which has already been suggested by a National Academy of Sciences panel report (Crowell and Burgess, 1996), could test combinations of arrest with greater use of supplementary measures such as battered women's shelters, detoxification centers for batterers, prosecution, counseling, and other strategies.

Juvenile Crime. Substantial federal funds are spent on policing juvenile crime, for which scientific evidence also shows that policing can increase crime under certain conditions. The effectiveness or harm resulting from federal support of juvenile policing cannot be determined from the present review, since the kinds of activities and kinds of offenders are too diverse. The available evidence, however, suggests that there is a substantial need for randomized controlled tests of federally funded juvenile policing strategies, in order to provide the greatest possible certainty that these programs at least do no harm. Federal support of juvenile curfew enforcement is of unknown effectiveness (and quantity), but the apparent growth of the idea suggests a need for rigorous program evaluation beyond the current NIJ-funded survey.

Other Programs. Federal support of policing in high-crime Weed and Seed target areas is strongly supported by the scientific evidence, as described above. Federal support of policing in the Comprehensive Communities Program is also supported by the evidence that extra police prevent crime more effectively in big cities.

Improving Effectiveness Through Stronger Evaluations

This analysis of how DOJ funding effectiveness shows many critical knowledge gaps. While the scientific evidence does suggest that the majority of DOJ funding for police is indeed effective at preventing crime, there is no evidence available on a large percentage of the other funding. A conservative estimate is that we lack even indirect scientific evidence on the effectiveness of some $500 million in Congressionally directed federal funding for local police in 1996. The record also suggests that evaluation results could help to revise and channel these funds in ways that would prevent crime more effectively. Moreover, the past two decades have seen police become much more sensitive to the significance of crime prevention evaluation results, and actively put them to good use (Blumstein and Petersilia, 1995).

Evaluation needs for each specific funding program have been noted above as appropriate. A basic statutory plan for accomplishing these evaluations more effectively is offered in Chapter Ten. The remainder of this chapter summarizes the evaluation needs of the current DOJ funding, and then addresses the highest priority areas for police effectiveness research implied by this review of the available evidence.

LLEBG Police Equipment and Technology. Historically, DOJ support of police technologies has focused on the engineering issues in accomplishing technological goals, rather than the human factors in using technology effectively. A major Congressional investment in human factors evaluations could provide the Congress with far better guidance on the effectiveness of its substantial appropriations in this area.

A prime example is NIJ's support of lighter-weight bullet-proof vests, which has apparently saved hundreds of police officers' lives. Even more lives might be saved, however, if evaluation research examined police officer compliance in wearing the vests, factors affecting that compliance, and strategies for increasing the compliance. Similar questions can be answered for the role of automated fingerprint identification systems (AFIS). The percentages of cases in which fingerprints are respectively sought, detected, submitted to an AFIS, resulting in a suspect's identification, leading to an arrest, conviction and incarceration can all be evaluated in a variety of police agencies. The results could encourage greater use of AFIS, if warranted, or if not, a redirection of federal funding into police expenditures that may be more cost-effective in preventing crime.

Another major example is police use of in-car computer terminals. In theory, this equipment can help patrol officers make far more productive us of the time they spend patrolling hot spots, or otherwise awaiting the next dispatch to a call for service. Whether the officers will actually use the terminals to look for stolen cars or check suspicious persons, however, is a key question for an equipment program evaluation. The National Institute of Justice can help design controlled tests (Scientific Methods Score = 5) randomly assigning new in-car computer systems to some officers but not others, with observations of how the officers spend their patrol time both before and after the new equipment is installed. This in turn could inform analyses of the number of arrests made per patrol hour, the number of guns seized, stolen cars recovered, and so on. Similar experiments could be done at the patrol beat level over longer periods of time, testing the hypothesis that beats patrolled by computer-equipped cars will have less crime than beats patrolled without them. If these hypotheses cannot be supported by rigorous scientific testing, additional research could identify the reasons the technology does not prevent crime as expected and possible ways to solve those problems.

Other possible examples of technology evaluations are limited only by the diverse array of police equipment already on the market and currently in development, from hand-held gun detectors revealing weapons concealed under clothing to electrical devices for police to shut off the ignition of pursued vehicles. A Congressional plan setting aside ten percent of program funding for controlled testing, and another ten percent for research costs, would allow evaluations to identify police technology and equipment of proven effectiveness.

Byrne Grant Multijurisdictional Task Forces Against Drugs. This program may be defined as serving purposes other than crime prevention. Other goals might be measured in amounts of drugs seized or the number of mid-level drug dealers arrested and incarcerated. Testing the effectiveness of these programs in accomplishing the goals might be done through random assignment of a large sample of cases to single jurisdiction versus task force investigation. Alternatively, before-and-after comparisons of drug abuse problems could be made in metropolitan statistical areas where the task forces operate, with further comparisons to areas not creating these task forces. Comparisons might also be made across task forces of different sizes. Basic productivity indicators could also be computed and compared across all Byrne-funded task forces, with an analysis of the reasons for variation in productivity. Further funding might then be conditional upon achieving specific productivity levels. Task force leadership might collaborate with NIJ researchers in framing a set of questions to be answered by such an evaluation, and agree upon scientifically and operationally appropriate means of designing an evaluation of this $190 million annual program.

Violence Against Women Grants. Both the STOP and Encourage Arrest grants have two critical areas in which program evaluation can help. One is discovering programs of proven effectiveness in preventing almost every kind of crime against women. The other is identifying the most effective means of delivering a wide array of support services, from police training to data banks. Both tasks are hindered by the fact that many of the grants awarded under these funding programs are under $20,000, and are too small in scope to warrant separate evaluations. This issue, which also applies to the Byrne Grants and is addressed in Chapter Ten, is one that a Congressional plan for evaluation can resolve. It is arguably inefficient for each grantee to confront similar issues separately, such as classroom instructional materials for police training. A national evaluation program to identify Violence Against Women programs of proven effectiveness would provide much better guidance for how to focus the thousands of small grants scheduled to be awarded by these programs in future years.

The methods of testing program effectiveness in crime prevention are discussed generally in Chapter Four. The most important police research issues concern the prediction and prevention of serious domestic violence, for which no scientifically validated risk assessment tools are currently available (Sherman and Strang, 1996). The effectiveness of police-monitored personal radio alarm necklaces for women given court orders of protection is a high priority for a randomized controlled trial. So is a comparison of the crime prevention effectiveness of misdemeanor domestic assault arrests with and without prosecution, which could indicate a need for Congressional earmarking of funding for the specific purpose of prosecution of such cases. Issuance of arrest warrants for absent misdemeanor assault offenders is a promising practice (Dunford, 1990) that needs replication. Various police responses to non-violent domestic disputes (which are more numerous than violent ones) can be compared and tested for their effectiveness in preventing subsequent violence.

Program effectiveness at accomplishing goals other than crime prevention can also benefit from evaluations. Improved gender equality and victim services in police actions can also be measured scientifically as program outcomes. Regardless of the effectiveness of mandatory arrest, for example, the literature reveals substantial difficulty in obtaining patrol officer compliance with arrest policies for misdemeanor assaults--of which the majority require no medical treatment and one-third have no visible signs of injury. The tendency of officers to trivialize these crimes, to respond slowly to domestic calls, and to refuse to make arrests are all behaviors that DOJ-funded training and technical assistance programs may seek to change. Whatever methods are used to pursue those goals, randomized controlled tests can reveal which methods are most effective. Followup observations of police treatment of women victims in the field would be a critically important--although expensive--component of evaluating training programs. Absent such careful scrutiny by a "big science" national evaluation effort, however, the effectiveness of programs for changing police behavior will remain unknown. Here again, a Congressional plan for developing programs of proven effectiveness could make a major difference.

Getting Guns Off the Streets--With Legitimacy. One major hypothesis about the declining homicide rate in the US is that police have become more effective at deterring illegal gun carrying in public places (Moore, 1980; Wilson, 1994). Further testing of the gun carrying hypothesis seems to warrant the highest priority for federal research, given the clear connection of guns to serious juvenile and gang violence. At the same time, the issue of police legitimacy and perceived harassment of young black males is a crucial aspect of gun enforcement. A research agenda developing both police effectiveness at detecting illegal guns, while enhancing police legitimacy in the eyes of all citizens including offenders, could address both issues simultaneously. On these issues, research could help reduce both homicides and riots, and increase general compliance with the law through greater respect for the moral authority of police.

Patrol Location and Timing Strategies. Since gun violence is heavily concentrated in less than 100 of the 10,000 police agencies reporting to the FBI, research is also needed on more general approaches to directed patrols in hot spots and hot times. One example is the apparently mundane is of police schedules, which may be vital to crime prevention. Police chiefs face enormous resistance from police unions in changing work assignments and schedules to concentrate police in high crime areas between 7 pm and 3 am, with the most officers assigned on weekends. Many must use overtime pay to even move in that direction. If experiments comparing crime-focused staffing patterns with conventional procedures found a reduction in crime, that could support police chiefs trying to make better use of taxpayer dollars.

Juvenile Shaming and Restorative Justice. Every police agency must deal with juvenile offenders. The Australian community accountability conferences can be tested in police agencies large and small. Given the negative findings about the effects of arrest on juvenile offending, there is much to be gained and perhaps little to lose by developing alternatives to arrest. The growing concern over serious juvenile violence, especially gun offenses in big cities, should not distort the truth that most juveniles are still arrested for shoplifting and other minor offenses. A program for first-offenders that works better to nip criminal careers in the bud may well prevent more serious property crime, such as auto theft, and violent crime. It may also increase police legitimacy in the eyes of the participating adults, far more effectively than conventional approaches to community policing.

Multi-Agency Experiments. The proposed Congressional restructuring of evaluations in Chapter Ten would make possible a major breakthrough in police research: comparing strategies across large sample of police departments. Random assignment of enhanced federal funding for specific strategies to half of the hundred largest cities could go a long way towards learning what works of agency-wide policies. A prime example is traffic enforcement. Proactive police arrests for drunk driving are generally sporadic (Ross, 1994), in part because there is no direct evidence that traffic deaths will rise if drunk driving arrests decline. Moreover, the evidence that traffic enforcement reduces robbery is suggestive but not conclusive. Taken together, the twin objectives of reducing traffic deaths and robberies would justify investment in a 100-agency randomized experiment in traffic enforcement. An experiment in which 50 police agencies selected at random from 100 volunteering agencies received substantial federal funding for greatly increased traffic enforcement--by 300 or 400%-- would be an ideal test of the hypothesis now weakly supported by merely correlational studies.

Another approach would go right to the core of the 1994 Crime Act--the 100,000 police. An experiment in which 20% more officers (over current levels including COPS grants) were randomly funded in half of a sample of police agencies would provide a far more definitive test of the crime prevention effectiveness of the $1.4 billion annual expenditure. The popular support for this program may render the question moot for the moment, but the question remains of just how effective the program is. Experiments using this design could also test other theories, such as problem-solving or community policing uses of extra officers.

Evaluation Funding Priorities. Over half of all DOJ funding for local crime prevention is directed to the police. The same cannot be said, however, for the allocation of program evaluation funding. The Congress has not addressed the question of evaluation funding priorities with the same clarity as it has identified program funding priorities. This is one more reason for the Congress to consider the restructuring of DOJ crime prevention evaluations as discussed in Chapter Ten.


1And in one case, the arrest of the entire Copenhagen police force by the Nazis in 1944, which was equivalent to a strike because the occupying German army did nothing to enforce civilian criminal laws before or after arresting the police (Andenaes, 1974).

2There was no difference in the self-reported offending data, but only 60% of the offenders gave followup interviews.

3Given the potential for vehicular homicide attached to drunk driving, that offense is included here in the definition of violent crime. It would not, however, be classified that way for most other purposes.

4These amounts are extrapolated from the Dunworth, et al (1997) analysis of the award of grants in 1989-94, proportionately applied to the FY 1996 allocation of $475 million.


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