SEVERAL TECHNIQUES HAVE BEEN USED TO ESTIMATE THE EFFECT OF POLICE ACTIVITIES ON THE INCIDENCE OF CRIME, INCLUDING: 1) CROSS-SECTIONAL ANALYSIS OF REPORTED CRIME RATES IN VARIOUS JURISDICTIONS AS COMPARED TO RESOURCES DEVOTED TO THE TOTALITY OF POLICE FUNCTIONS OR CERTAIN POLICE FUNCTIONS, 2) LONGITUDINAL ANALYSIS OF A TIME SERIES OF CRIME INCIDENCE IN SEVERAL JURISDICTIONS OR IN A SINGLE JURISDICTION WHERE POLICE DEPLOYMENT OR OPERATIONS CHANGED OVER TIME, AND 3) EXPERIMENTAL MANIPULATION OF THE NATURE OR AMOUNT OF POLICE ACTIVITIES. NEARLY EVERY STUDY CONCERNING DETERRENCE HAS BEEN SUBJECTED TO CRITICISM FOR ONE OR MORE FAULTS, SUCH AS FAILURE TO DISTINGUISH BETWEEN TRUE AND REPORTED CRIME RATES, FAILURE TO SPECIFY OR MAINTAIN THE EXPERIMENTAL CONDITIONS, APPARENT ERRORS IN THE DATA, OR CONFUSION BETWEEN CAUSE AND EFFECT. THIS REVIEW INDICATES THAT MOST STUDIES ARE CONSISTENT WITH THE VIEW THAT A SUBSTANTIAL INCREASE IN POLICE ACTIVITY WILL REDUCE CRIME FOR A PERIOD OF TIME, BUT IN THE REAL WORLD INCREASES IN POLICE MANPOWER TEND TO FOLLOW INCREASES IN CRIME. THE MAGNITUDE AND DURATION OF DETERRENCE EFFECTS ARE ESSENTIALLY UNKNOWN, THE AUTHOR STATES. (AUTHOR ABSTRACT)...DMC