Press, S.J. (1971). Some Effects of an Increase in Police Manpower in the 20th Precinct of New York City. Santa Monica, CA: RAND Corporation.
Location in the Matrix; Methodological Rigor; Outcome:
Neighborhoods, General, Reactive, Moderately Rigorous; Effective
What police practice or strategy was examined?
This study examines the impact of increasing police manpower on crime.
How was the intervention evaluated?
Police manpower assigned to the 20th precinct in Manhattan was increased by approximately 40 percent in October 1966, and a study was conducted to determine the effect of the additional manpower on reported crime rates. The study examined only the increase in number of officers, not the ways in which the additional officers were deployed. Three other precincts in the city (18, 22, 24) were selected post-facto to serve as controls. Both report and arrest data were examined for a five-year period (1963-1967) encompassing both pre and post-intervention periods. Ten crimes were analyzed, including both felonies and misdemeanors, and arrest statistics were calculated.
What were the key findings?
In most cases, crime increased in the control precincts. While crime also increased in the 20th precinct, the increase was smaller so that the net change was a decline in crime. For all felonies there was a net decrease of 24.11 crimes per week. Felony arrests experienced a net increase of 1.21 arrests per week. Net changes for total misdemeanors were not significant. The strongest suggestion of displacement was found in adjacent Central Park where major crime types increased during the experiment, but generally by an amount less than the decrease observed in the 20th precinct.
What were the implications for law enforcement?
The author suggests caution in interpreting the results, but the decreases in reported felonies and simultaneous increases in arrests for reported felonies suggest increased police manpower was an effective deterrent to the commission of felonies.
Where can I find more information about this intervention, similar types of intervention, or related studies?