Di Tella, R., & Schargrodsky, E. (2004). Do police reduce crime? Estimates using the allocation of police forces after a terrorist attack. The American Economic Review, 94(1), 115-133.
Location in the Matrix; Methodological Rigor; Outcome:
Micro places, General, Reactive; Rigorous; Effective
What police practice or strategy was examined?
The study examined the effect of increased police presence on crime. In 1994 in Buenos Aires, one week after a terrorist bombing at the city’s main Jewish Center, the government assigned 24-hour police protection to more than 270 Jewish and Muslim institutions in the country. This provides researchers with the ability to compare specific locations where increased police presence occurred with comparison locations that did not receive the same police presence. The focus of this study was on the impact of police presence on auto theft.
How was the intervention evaluated?
The study selected three noncontiguous, Buenos Aires neighborhoods for the analysis. Target blocks were those within the distance of two blocks away from a protected institution, while comparison blocks were those more than two blocks away from the protected institution. The authors collected police data regarding auto theft in these neighborhoods for the nine-month period from April 1, 1994 to December 31, 1994. April 1 to July 17 constitutes the period before the attack, and then August 1 to December 31 covers the period of police protection. The study also controlled for the distance of each block to the nearest Jewish institution within the target group by distinguishing blocks that contain a Jewish institution, blocks contiguous to a block containing a Jewish institution, and blocks two blocks away from a block containing a Jewish institution and comparing them with the comparison blocks (more than two blocks away). To determine treatment effect, the authors compared the auto theft rate before and during the intervention in the target and comparison group.
What were the key findings?
The introduction of fixed and observable police presence generated a significant decline in car thefts in the protected blocks (those containing a Jewish institution) by 75% but no effect one or two blocks away relative to streets more than two blocks away.
What were the implications for law enforcement?
The authors suggest that a posted and visible police guard exerts a large, negative, local effect (only on blocks with police physical presence) on auto theft but little or no effect outside a narrow area.
Where can I find more information about this intervention, similar types of intervention, or related studies?