On October 6, Mitchell Weinzetl, a hired consultant from the International Associations of Chiefs of Police, had no interest in sugarcoating it—he believed the racial disparity studies concerning the Durham Police Department had “material flaws.”
At the time, that assertion, however, did not sit well with many members of the Durham City Council.
Councilwoman Jillian Johnson questioned Weinzetl’s assessment of the studies—a task conducted by the former chief of police of a small city in Minnesota for $91,323.
Weinzetl told Johnson and the rest of the council he “wasn’t in a position to say [racially biased practices] aren’t occurring,” but instead believe the studies that determined there were disparities had “extraneous variables.”
Needless to say, Johnson wasn’t convinced. “So what you’re saying is that you didn’t find evidence [of racially discriminatory policing], but also that you think that these two studies that did find evidence are flawed. I’m questioning whether your expertise is equal to that of the people who did those studies.”
Now RTI International, one of the organizations that produced a study about racial disparities in traffic stops conducted by DPD, is refuting the IACP’s claims that there were material flaws in its “veil of darkness” analysis, a study that was requested by
In a statement provided to the INDY from RTI International’s Travis Taniguchi, the lead research criminologist at RTI and the study’s lead author said, “The veil of darkness (VOD) analysis used by RTI International to assess racial disparity in the DPD traffic stop data has been used in dozens of jurisdictions and reported in at least six peer-reviewed publications. It is widely considered one of the best available methods for understanding and exploring potential racial disparity in traffic stop data. Like any methodology, it is not without its limitations. These limitations, however, are highlighted clearly in the original report and we make no claims beyond what the data and methods are able to tell us.”
The rest of the statement reads:
The IACP report claimed that the VOD analysis seeks to determine whether the police stop a greater percentage of black motorists during the day, when officers can more readily identify the race of drivers. This is partially accurate. The comparison made is between a limited range of times during which it is sometimes dark (e.g., 6 p.m. in winter months) but light during other times. Focus on this time range, referred to as the intertwilight period, avoids issues of vastly different driving populations that may be on the road in daytime and nighttime. Framing the comparison as day versus not-day is inaccurate, as the same times of day are being compared throughout the analysis.
The IACP report fails to specify the material flaws it claims are in our analyses or conclusions about the DPD’s traffic stop data. Instead, the issues raised about the methodology stem from a fundamental misunderstanding of the processes employed. Traditional methodologies to assess racial disparities in traffic stops require an external benchmark, such as the percentage of minority residents in an area, to serve as a comparison against the racial composition of those who are stopped by the police. However, these external benchmarks are problematic, as detailed in our original report, and there is good reason to avoid analytical methods that rely on them. Because we are comparing citywide traffic stop data at different points in time, there is no need to specify an external benchmark that varies by location.
The concentration of police deployment is, in a practical sense, also irrelevant to RTI’s analysis. The VOD methodology is centered on a conceptual argument that officers can more readily determine driver race during daylight than in darkness. To reduce the variability in driver population, the methodology considers only the time period when it is sometimes dark during the year and sometimes light during the year. For police deployment practices to “matter,” one would have to postulate that police deployment (and more importantly traffic stop activity) was conditional upon daylight. The key here is that deployment has to be conditional upon lighting, not time of day. In other words, one would need to argue that deployment practices were systematically different depending upon how much daylight is available. This is an implausible argument and one of the key reasons that the VOD approach has been so well supported by criminologist.
We find no validity in the criticisms leveled by Dr. Weinzetl and believe that the IACP has made fundamental errors in their criticisms of RTI’s analysis. We stand behind the methodology, its implementation on DPD data, and the conclusions drawn from the analysis.
RTI International isn’t just some research institute. It’s one of the world’s leading research institutes. And while the IACP study had some good ideas on staffing issues in the department, it was clear that it didn’t take a harder look at the data presented by RTI.