UC Berkeley

This Dissertation consists of three empirical applications on the economics of crime and law enforcement.

Chapter 1 uses over 200,000 patrol stops conducted by the Oakland Police Department to estimate differences in policing behavior among black, white, Hispanic, and Asian officers. In contrast to previous studies which consider average differences at the city or state level, this study uses individual officers' patrol assignments and the exact date, time, and geographic coordinates of each stop to identify between-officer differences.

The data indicate little to no differences across officer race on average, but substantial differences within neighborhoods. In general, minority officers less intensely police all races in minority neighborhoods, but more intensely police all races in white neighborhoods relative to their white officer peers.

A model of police behavior with imperfect information offers one explanation for this result. In the model, an unbiased officer with relatively high ability to interpret suspect behavior polices with relatively low intensity. The observed outcomes are then consistent with officers possessing neighborhood-specific informational advantages in policing, particularly with respect to their own race. That is, minority officers better interpret suspect behavior in minority neighborhoods, while white officers better interpret suspect behavior in white neighborhoods. Simulation results suggest that small differences in interpretative ability (modeled as noise in signals observed by the officer) can generate the observed magnitudes.

Chapter 2, which is coauthored with Justin McCrary, presents evidence from six data sets on the participation of youth in crime near the age of criminal majority. The evidence suggests smooth behavior through the transition to adulthood, despite substantial changes in punitiveness, and is consistent with small deterrence effects of long prisons sentences for young offenders.

Chapter 3 reconsiders the empirical analysis of Knowles, Persico, and Todd (2001). Knowles, Persico, and Todd (2001) presents a model of police and motorist behavior in the context of vehicle searches, and tests it using data from Maryland. The main implication of the Knowles et al. model is that in the absence of racial discrimination, the proportion of searches yielding drugs (or ''hit rate'') will be equated across races. A relatively low hit rate for any group suggests that police may improve their overall hit rate by shifting resources away from that group, and is thus evidence toward discrimination. Using data on vehicle searches by Maryland State Police, they find no bias against blacks relative to whites, but significant bias against white females and particularly Hispanics.

However, while their study focused on searches occurring along Interstate 95, this study considers all vehicle searches in Maryland, both for the time period studied in Knowles, Persico, and Todd (2001) (1995--1999) and in more recent years (1995--2006). The main results suggest substantially lower hit rates for blacks for searches occurring off Interstate 95, though almost no difference for searches on Interstate 95.