Law enforcement agencies continue to be the best available and most widely used source of information for national gang surveys and other forms of criminal justice research. Criminal justice agencies usually are centrally organized and capable of developing systems for routine recordkeeping and reporting (Curry, 1995; Maxson, Klein, and Cunningham, 1993). However, law enforcement data have some important limitations. First, many agencies do not collect data in a standardized manner. Databases, automated or otherwise, are becoming more widespread, but are more commonly used for gathering intelligence than for recording crime. In addition, the accuracy of responses to surveys of law enforcement agencies often varies across jurisdictions, because responses are generally based on estimates. For this survey, instructions specifically asked the respondent to base responses on records or personal knowledge. To determine the extent to which personal knowledge or estimates were used, the survey asked respondents to identify the source of their responses. The majority of respondents (53 percent) said they used both official records and estimates, while 44 percent indicated that they reported only estimates. Only 2 percent of respondents indicated that their responses were derived solely from official records.

Second, responses to survey questions likely were influenced by the respondents' perceptions of gangs in their jurisdiction. Each year, the survey is directed to the previous year's respondent or, if the agency has not responded to earlier surveys, to the chief of police or sheriff. Unfortunately, it is difficult to ensure that the same respondent or even the most appropriate official receives and responds to the survey. As a result, a number of different perceptions and opinions may be reflected in the responses of some jurisdictions. Political considerations also may affect responses, and a gang problem may be either denied or exaggerated (Curry, 1995).

Definitions continue to pose problems for practitioners and researchers evaluating gang activity on a national level. Little agreement has been reached on what constitutes a gang, gang member, or gang incident, despite efforts to gain a consensus (Spergel and Bobrowski, 1989). In light of these problems, the current survey did not seek to define gang terms narrowly. The survey defined a youth gang as "a group of youths or young adults in (the respondent's) jurisdiction that (the respondent) or other responsible persons in (the respondent's) agency or community are willing to identify or classify as a 'gang.'" Respondents were asked to exclude motorcycle gangs, hate or ideology groups, prison gangs, and exclusively adult gangs. Respondents were also provided with two definitions of gang crime in order to gain some consistency in the reporting of homicides (see appendix A).