Racial bias in police shootings

I used the Washington Post data on 1499 killings of Americans by police officers in 2015 and July 2016 to analyze the following question:

Are African Americans who are killed by police officers more likely to be unarmed than non African Americans killed by police?  I am interested in this specific question because answering it gives a fairly clear indication if African Americans are treated differently when they encounter police.  One concern about racial bias is that police may (knowingly or unknowingly) be more likely to interpret a situation as dangerous depending on characteristics of the person they encounter.  If we assume that African Americans and non African Americans are equally likely to be armed in any encounter with police (it’s hard to know if this assumption is true) then any difference in the probability of being shot and killed by police might depend on how the officer is interpreting the situation, and may reflect a racial bias.

The analysis is simple.  I predicted the log-odds of being armed (classified two different ways: one as armed vs. unarmed and one as armed vs. unarmed or armed with a toy weapon) as a function of race (either African American or Other) using logistic regression.  I threw in ‘signs of mental illness’ and ‘gender’ into the model as well, but they aren’t consequential.  If you don’t care about the statistics, skip to the interpretation section below.

Results

The results for predicting the log-odds ‘unarmed’ or ‘toy weapon’

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The results for predicting the log-odds ‘unarmed’

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Converting the predicted log odds into a probability, we get:

Probability (as %) of an African American being armed when killed by police: 64.1%

Probability (as %) of a non African American being armed when killed by police: 71.0%

I ran the same analysis using data from the Mapping Police Violence site (based on their classification of unarmed), and found roughly the same effect:

results5

Interpretation

Based on these data (which are publicly available and can be openly scrutinized) the results are unequivocal: African Americans who are killed by police are about 7% less likely to be armed than non African Americans killed by police.  Perhaps this is because African Americans are less likely to be armed in police encounters when compared to non African Americans.  It may also reflect a racial bias in the interpretation of danger by police officers.  Keep in mind that this analysis implicitly controls for any differences in the rates of crime by ethnic status; all the subjects in the analyses were shot and killed by police, but African Americans were simply less likely to be armed.