Searching for the Denominator: Problems with Police Traffic Stop Data and an Early Warning System Solution

Abstract

In response to widespread allegations of racial and ethnic discrimination in traffic stops, a practice that has been labeled “racial profiling,” law enforcement agencies are now collecting data on traffic stops that include the race or ethnicity of drivers. Interpreting these data to determine whether a pattern of race discrimination exists poses enormous difficulties. Specifically, it is not clear what baseline (often referred to as “the denominator”) should be used to assess the racial and ethnic distribution of people stopped. Using the first traffic stop data reports from the San Jose Police Department as a case study, this paper examines baselines that are commonly used or discussed as appropriate. The paper argues that resident population data and/or official crime data are not adequate as baselines. As an alternative, the paper proposes an approach based on police early warning systems.

Book Review: Franklin E. Zimring, When Police Kill

“…The use of census data as a "benchmark" (i.e., denominator) for police behavior has been criticized by scholars (e.g., Nix et al, 2017;Walker, 2001), but as Zimring points out, arrest data may not be appropriate either. Without an appropriate benchmark, it is difficult to make sense of the observed demographic differences in police killings.…”

Racial profiling : using propensity score matching to examine focal concerns theory.

“…First, it can expose officers who have a higher number of traffic stops and determine if the number of stops indicates a problem (Walker, 2001). Second, the department may realize variations in enforcement practices between various shifts (Walker, 2001). The final benefit is that it may show that some male officers have a high number of stops involving female drivers (Walker, 2001).…”

“…Second, the department may realize variations in enforcement practices between various shifts (Walker, 2001). The final benefit is that it may show that some male officers have a high number of stops involving female drivers (Walker, 2001). …”

“…First, it can expose officers who have a higher number of traffic stops and determine if the number of stops indicates a problem (Walker, 2001). Second, the department may realize variations in enforcement practices between various shifts (Walker, 2001).…”

“…It "warns" by placing an officer on a list showing that the officer is in need of special attention by his or her supervisor, or that some other intervention is warranted. Identified officers are sent to some kind of intervention, usually counseling or training designed to correct the problematic behavior (Alpert, 2007;; U.S. Department of Justice, 2001;Walker, 2001;Walker, Alpert, & Kenney, 2000). Identifying problem officers will help police departments provide better service and maintain a positive image and relationship with the community.…”