Reconsidering Racial Bias in Motor Vehicle Searches: Theory and Evidence

Abstract

In an influential paper in the February 2001 Journal of Political Economy, Knowles, Persico, and Todd 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. (For recent studies, see Hernandez-Murillo and Knowles [2004], Levitt [2004], Anwar and Fang [2006], Dominitz and Knowles [2006], and Persico and Todd [2006].) 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 the Maryland State Police (MSP), they find no bias against blacks relative to whites but significant bias against white females and particularly Hispanics (though both groups had limited observations: 41 white females and 97 Hispanics). 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. Since