Racial profiling in L.A.: the numbers don’t lie

Ian Ayres is a professor at Yale Law School and the author of "Super Crunchers: Why Thinking-By-Numbers Is the New Way to Be Smart."

On monday, the ACLU of Southern California released a report analyzing more than 700,000 cases in which Los Angeles Police Department officers stopped pedestrians and/or drivers of motor vehicles between July 2003 and June 2004.

The study, which I wrote with my research assistant, Jonathan Borowsky, asked not simply whether African Americans and Latinos are stopped and searched by the LAPD more often than whites -- it’s clear that they are -- but the more complex question of whether these racial disparities are justified by legitimate policing practices, such as deciding to police more aggressively in high-crime neighborhoods.

We found persistent and statistically significant racial disparities in policing that raise grave concerns that African Americans and Latinos in Los Angeles are, as we put it in the report, “over-stopped, over-frisked, over-searched and over-arrested.” After controlling for violent crime rates and property crime rates in specific neighborhoods, as well as a host of other variables, we found the following:


For every 10,000 residents, about 3,400 more black people are stopped than whites, and 360 more Latinos are stopped than whites. Stopped blacks are 127% more likely to be frisked -- and stopped Latinos are 43% more likely to be frisked -- than stopped whites.

Stopped blacks are 76% more likely to be searched, and stopped Latinos are 16% more likely to be searched than stopped whites.

Stopped blacks are 29% more likely to be arrested, and stopped Latinos are 32% more likely to be arrested than stopped whites.

Now consider this: Although stopped blacks were 127% more likely to be frisked than stopped whites, they were 42.3% less likely to be found with a weapon after they were frisked, 25% less likely to be found with drugs and 33% less likely to be found with other contraband. We found similar patterns for Latinos.

Not only did we find that African Americans and Latinos were subjected to more stops, frisks, searches and arrests than whites, we also found that these additional police actions aren’t because of the fact that people of color live in higher-crime areas or because they more often carry drugs or weapons, or any other legitimate reason that we can discern from the rich set of data we examined.

Police Chief William J. Bratton quickly rejected these findings, primarily because the study used data that was more than 4 years old. This is a fair point. But we had no other choice: The department has not released the more recent stop data that it has been collecting, nor has it analyzed the more recent data to test for racial disparities. If Bratton is truly confident that unjustified racial disparities are a thing of the past, he should be able to show the change in the current data. I would be happy to organize a group of respected academics to help analyze it.


Bratton also asserted that the report was flawed because we failed to control for the race of both officers involved in the stop. On this point, Bratton is simply wrong about how to conduct a statistical analysis. When testing for unjustified racial disparities in who is stopped by the police in cars and on the street, it’s inappropriate to control for the race of either of the officers. The likelihood of being stopped, frisked or arrested shouldn’t turn on whether a black, Latino or white officer was involved.

As an ancillary test -- after we’d calculated the general disparities -- we did look at the officers involved, and we found that the racial disparities in the likelihood of arrest were substantially lower when at least one of the stopping officers was the same race as the suspect.

For example, we found that the black arrest disparity was 9 percentage points lower when at least one of the stopping officers was black. Bratton should be troubled that there is less disparity when the officer is the same race as the person stopped, as that result adds credibility to the idea that the disparities in different-race interactions may be because of racial bias.

The president of the Los Angeles Police Protective League, Tim Sands, even more harshly rejected the results of our report. Sands said I appeared to start with my conclusions and then “worked data to fit.” This is a vague charge, but one way to respond to the concern is with transparency. I’ve posted the data I used in the report and the associated statistical files to the Internet so that other academics can easily double-check the report’s analysis.

Sands has argued that the results are not valid because officers often don’t know the race of the suspect when they decide to pull over a car. That may or may not be true. But our study looked not just at motor vehicle stops but at pedestrian stops as well, which also showed racial disparities. We also found that, once people were stopped, officers were more likely to frisk, search or arrest African Americans and Latinos than whites. At the point of making these decisions, officers can certainly see the apparent race of the suspects.

It is particularly telling that neither Bratton nor Sands responded to the evidence that the frisks and searches of minorities systematically produced less evidence of crime than the frisks and searches of whites. It is implausible that higher frisk and search rates are justified by higher minority criminality, when these frisks and searches are substantially less likely to uncover weapons, drugs or other types of contraband. Independent of racial disparity, it is a sign of ineffective policing to have officers engage in such a large number of fruitless searches.


Sands charges that I cannot use data to “prove what 9,700 individual officers are thinking when they make traffic stops.” But if he thinks that is what I tried to do, he seriously misreads the report. I never suggested that the data show what an officer might be thinking, and I was careful not to attribute the disparities to conscious discrimination on the part of individual officers.

What the report finds is that there are statistically significant racial disparities in a variety of police behaviors that are not explained by legitimate police concerns such as the local crime rate -- or, in the cases of frisks and searches, the likelihood of actually uncovering contraband.

My inability to probe the minds of officers does not make my results less important. The report shows that people of color in Los Angeles experience harsher treatment by police that doesn’t appear to be justified by any legitimate law enforcement concerns. The LAPD can’t just deny that racism is involved and let the matter rest; it should take steps to address that inequality.

So what does this all mean? The LAPD should be more open to evidence-based policing. Bratton, with good reason, extols data-driven policing when it comes to detecting emerging patterns of crime. The department already has an early warning system to identify officers with troubling patterns of uses of force or civilian complaints, but that system doesn’t address racial disparities, even though the data to do so are available. The department must be as open to the same kinds of statistical analysis when it comes to tests of racial disparity.