Tuesday, 12 July 2016

An empirical analysis of racial differences in police use of force

A timely new NBER working paper.

An Empirical Analysis of Racial Differences in Police Use of Force
Roland G. Fryer, Jr
NBER Working Paper No. 22399
Issued in July 2016
NBER Program(s): LE LS POL
The abstract reads:
This paper explores racial differences in police use of force. On non-lethal uses of force, blacks and Hispanics are more than fifty percent more likely to experience some form of force in interactions with police. Adding controls that account for important context and civilian behavior reduces, but cannot fully explain, these disparities. On the most extreme use of force – officer-involved shootings – we find no racial differences in either the raw data or when contextual factors are taken into account. We argue that the patterns in the data are consistent with a model in which police officers are utility maximizers, a fraction of which have a preference for discrimination, who incur relatively high expected costs of officer-involved shootings.
In the introduction to the paper Fryer writes,
The results obtained using these data are informative and, in some cases, startling. Using data on NYC’s Stop and Frisk program, we demonstrate that on non-lethal uses of force – putting hands on civilians (which includes slapping or grabbing) or pushing individuals into a wall or onto the ground, there are large racial differences. In the raw data, blacks and Hispanics are more than fifty percent more likely to have an interaction with police which involves any use of force. Accounting for baseline demographics such as age and gender, encounter characteristics such as whether individuals supplied identification or whether the interaction occurred in a high- or low crime area, or civilian behaviors does little to alter the race coefficient. Adding precinct and year fixed effects, which estimates racial differences in police use of force by restricting to variation within a given police precinct in a given year reduces the black coefficient by 19.4 percent and the Hispanic coefficient by 26 percent, though both are still statistically larger than zero. Including more than 125 controls available in the data, the odds-ratio on black (resp. Hispanic) is 1.173 (resp. 1.120).

Interestingly, as the intensity of force increases (e.g. handcuffing civilians without arrest, drawing or pointing a weapon, or using pepper spray or a baton), the probability that any civilian is subjected to such treatment is small, but the racial difference remains surprisingly constant. For instance, 0.26 percent of interactions between police and civilians involve an officer drawing a weapon; 0.02 percent involve using a baton. These are rare events. Yet, the results indicate that they are significantly more rare for whites than blacks. In the raw data, blacks are 21.3 percent more likely to be involved in an interaction with police in which at least a weapon is drawn than whites and the difference is statistically significant. Adding our full set of controls reduces the racial difference to 19.4 percent. Across all non-lethal uses of force, the odds-ratio of the black coefficient ranges from 1.163 (0.036) to 1.249 (0.129).

Data from the Police-Public Contact Survey are qualitatively similar to the results from Stop and Frisk data, both in terms of whether or not any force is used and the intensity of force, though the estimated racial differences is larger. In the raw data, blacks and Hispanics are approximately two percentage points more likely than whites to report any use of force in a police interaction. The white mean is 0.8 percent. Thus, the odds ratio is 3.335 for blacks and 2.584 for Hispanics. As the use of force increases, the racial difference remains roughly constant. Adding controls for civilian demographics, civilian behavior, contact and officer characteristics, or year does little to alter the results. The coefficients are virtually unchanged and are all highly significant with the exception of the highest uses of force for which data is sparse.

There are several potential explanations for the quantitative differences between our estimates using Stop and Frisk data and those using PPCS data. First, we estimate odds-ratios and the baseline probability of force in each of the datasets is substantially different. Second, the PPCS is a nationally representative sample of a broad set of police-civilian interactions. Stop and Frisk data is from a particularly aggressive form of policing in a dense urban area. Third, the PPCS is gleaned from the civilian perspective. Finally, granular controls for location are particularly important in the Stop and Frisk data and unavailable in PPCS. In the end, the “Truth” is likely somewhere in the middle and, importantly, both bounds are statistically and economically important.

In stark contrast to non-lethal uses of force, we find no racial differences in officer-involved shootings on either the extensive or intensive margins. Using data from Houston, Texas – where we have both officer-involved shootings and a randomly chosen set of potential interactions with police where lethal force may have been justified – we find, in the raw data, that blacks are 23.8 percent less likely to be shot at by police relative to whites. Hispanics are 8.5 percent less likely. Both coefficients are statistically insignificant. Adding controls for civilian demographics, officer demographics, encounter characteristics, type of weapon civilian was carrying, and year fixed effects, the black (resp. Hispanic) coefficient is 0.924 (0.417) (resp. 1.256 (0.595)). These coefficients are remarkably robust across alternative empirical specifications and subsets of the data. Partitioning the data in myriad ways, we find no evidence of racial discrimination in officer-involved shootings. Investigating the intensive margin – the timing of shootings or how many bullets were discharged in the endeavor – there are no detectable racial differences.

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