Things DoJ doesn’t know about racial disparities in Ferguson
On February 10, 2016, the Department of Justice filed a lawsuit against the City of Ferguson, Missouri alleging that the City’s police and court practices violate the due process clause of the Constitution and had an unlawful disparate impact on the City’s African American residents. The two claims have an unusual relationship.
The former claim involves what DOJ regards as a range of unjustified practices that cause the city to issue too many citations and too many arrest warrants for things like failure to make a scheduled fine payment or missing a court appearance. The latter claim involves the fact that African Americans make up a much higher proportion of persons receiving citations and arrested pursuant to outstanding warrants than the 67 percent they make up of Ferguson’s population. What the DOJ fails to understand, however, is that reducing the number of citations and arrest warrants will tend to increase, not decrease, the proportion African Americans make up of persons cited and arrested.
In a January 28, 2014 post on the Hill’s Congress blog titled “Things government doesn’t know about racial disparities,” I illustrated a key element of DOJ’s failure to understand data on racial differences. I posited a situation where pass rates on a test are 80 percent for whites and 63 percent for a minority group and thus the pass rate was 27 percent higher for whites than minorities. If the cutoff is lowered to the point where 95 percent of whites pass, assuming normal test score distributions, the minority pass rate would be about 87 percent. With the lower cutoff, the pass rate would be only 9 percent higher for whites than minorities. This is why lowering cutoffs is generally regarded as a means of reducing a test’s racial impact.
But while lowering a cutoff tends to reduce relative (percentage) differences in pass rates, it tends to increase relative differences in fail rates. In the situation above, the minority fail rate was initially 1.85 times the white fail rate (37 percent/20 percent). With the lower cutoff, the minority fail rate would be 2.6 times the white fail rate (13 percent/5 percent).
The pattern is essentially universal. Relaxing any standard and thereby reducing the frequency of an adverse outcome, while tending to reduce relative differences in rates of avoiding the outcome, tends to increase relative differences in rates of experiencing the adverse outcome. DOJ, however, has yet to understand this. It has pressured lenders to relax lending standards and public schools to relax discipline standards precisely in order to reduce relative racial differences in adverse borrower outcomes and adverse discipline outcomes. Unaware that reducing adverse outcomes tends to increase, not reduce, relative racial differences in rates of experiencing the outcomes, DOJ continues to monitor the fairness of practices on the basis of relative differences in adverse outcomes. Thus, by acceding to DOJ pressure to relax standards, lenders and schools increase the chances that DOJ will sue them for discrimination.
A corollary to the pattern whereby reducing the frequency of an outcome will tend to increase relative differences in rates of experiencing the outcome is a pattern whereby reducing the frequency of an outcome will tend to cause more susceptible groups to make up larger proportions of those experiencing the outcome than they previously did. In the test score hypothetical, assuming minorities made up 67 percent of test takers, they would make up79 percent of those who failed at the higher cutoff and 84 percent of those who failed at the lower cutoff. Similarly, reducing citations and arrests will tend to increase the proportion African Americans make up of persons cited and arrested. By way of an obvious example, increasing the number of missed payments or missed court appearances necessary to trigger issuance of a warrant – something the due process portion of the DOJ complaint suggests Ferguson does far too readily – will tend to increase the proportion African Americans make up of persons against whom such warrants are issued.
The DOJ complaint also maintains that one basis to infer that the City’s actions were racially motivated is the fact that the City continued its practices notwithstanding the magnitude of the racial impact. As explained above, however, the DOJ has no idea how to appraise the magnitude of a racial impact or the relationship of the magnitude of the impact to particular practices. If the case ever gets tried, it may provide a useful forum for addressing both the measurement issues themselves and the implications of the government’s failure to understand them.
Scanlan is a lawyer based in Washington, DC.