Reconsidering Racial Bias in Motor Vehicle Searches: Theory and Evidence

Abstract

Knowles, Persico, and Todd (2001) present a model of police and motorist behavior in the context of vehicle searches and test it using data from Maryland. Their work marked a resurgence in interest on how to interpret purported evidence of statistical and racial discrimination. The main implication of the their 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 the Maryland State Police (MSP), they find no bias against blacks relative to whites but significant bias against white females and particularly Hispanics.

In this paper, I reconsider the Knowles et al. analysis. An important feature of the data used by Knowles et al. is that they are limited to searches occurring on Interstate 95, which was also the focus of the racial profiling lawsuit filed against the MSP in 1993. However, while the suit focused on I-95 searches, the settlement required the MSP to record all vehicle searches, of which I-95 searches constitute about one-third. When considering all MSP searches, I find evidence toward racial discrimination against blacks and especially Hispanics, and that these disparities have increased in recent years.

Keywords: Racial bias, law enforcement

JEL Classification: J71, K42