A Time-Series Analysis of Crime, Deterrence, and Drug Abuse in New York City

Theft and Deterrence

“…For example, in monthly data, an increase in the police force in a given month will affect criminal activity in the same month, but an increase in crime cannot alter the size of the police force in that same month because of the much longer lag between a policy decision to increase the working police force and the actual deployment of police officers on the street. This identification strategy has been employed by Corman andMocan (2000, 2005). The third strategy is to find a natural experiment which generates a truly exogenous variation in deterrence, as in Di Tella and Schargrodsky (2004), who use the increase in police protection around Jewish institutions in Buenos Aires after a terrorist attack to identify the impact of police presence on car thefts, and Drago, Galbiati and Vertova (2009) Although these empirical strategies have permitted researchers to refine and improve upon earlier estimates, a convincing natural experiment is very difficult to find, the validity of any instrumental variable can always be questioned, and one can argue that if policy makers have foresight about future crime rates, low frequency data could also suffer from simultaneity bias.…”

Deterrence works for criminals

“…The underlying assumption that individuals react to incentives and changes in expected payoffs constitutes the deterrence hypothesis. A number of empirical tests of the deterrence hypothesis have been criticized for their estimation techniques and issues of simultaneity, data collection, data aggregation, and possible incapacitation bias (Levitt and Miles, 2007; notable exceptions include Levitt, 1997;Corman and Mocan, 2000;Fisman and Miguel, 2007).…”

What Works in Reducing Hooliganism?

“…As stressed by Purdum (1990) "even if Mayor David N. Dinkins agrees next week, as expected, to hire thousand of new police officers for New York City, the process of recruiting and training them is so complex that the last of them would probably not ready for duty on the streets for the two years, with luck." Corman and Mocan (2000) take advantage of the fact that new police officers are required to attend a six-months course at the Police Academy before their effective deployment to eliminate simultaneity issue between police and crime.…”

“…Our analysis also rely on a centralized policy intervention, as in Evans and Owens (2007), but we also exploit documented delays between the time the hiring procedures started and the time the newly recruited police officer become operational, as in Corman and Mocan (2000). Italian recruiting procedures have some advantages over the one based on the COPS program analyzed in Evans and Owens (2007): i) local police offices do not need to apply to hire more officers; ii) several years pass between the centralized financial decision to increase the number of police forces and the actual hiring making it less likely that hirings depend on expected changes in crime rates; the relative changes in police forces that are driven by our centralized hiring system tend to be larger.…”