Racial bias in the use of force by police

16 May, 2021 at 23:22 | Posted in Theory of Science & Methodology | 3 Comments

UN Committee condemns U.S. for racial disparity, police brutality | PBS  NewsHourOur analysis indicates that existing empirical work in this area is producing a misleading portrait of evidence as to the severity of racial bias in police behavior. Replicating and extending the study of police behavior in New York in Fryer (2019), we show that the consequences of ignoring the selective process that generates police data are severe, leading analysts to dramatically underestimate or conceal entirely the differential police violence faced by civilians of color. For example, while a naïve analysis that assumes no race-based selection into the data suggests only 10,000 black and Hispanic civilians were handcuffed because of racial bias in New York City between 2003 and 2013, we estimate that the true number is approximately 56,000. And while analyses ignoring bias in stopping would conclude that 10% of uses of force against black and Hispanic civilians in these data were discriminatory, after bias-correction, we estimate that the true percentage is 39% …

Traditionally, analysts use data on stopped individuals to study bias by computing the difference in violence rates between stopped minority and white civilians, while controlling for observable differences between these two sets of encounters. We term this the “naïve estimator” … However, without further assumptions, this quantity will have no causal interpretation so long as the treatment affects the mediator (i.e., civilian race affects whether officers detain a civilian). As we show below, this is because treated encounters (with minority civilians) that result in a stop will not be comparable to those with stopped control (majority) civilians. As a simple example, suppose officers exhibited racial bias as follows: they detain white civilians if they observe them committing a serious crime (such as assault, potentially warranting the use of force) but detain nonwhite civilians regardless of observed behavior. When this is true, comparing stopped white and nonwhite civilians amounts to comparing fundamentally different groups. The analyst will observe force used against a greater proportion of stopped white civilians because of the differential physical threat they pose to officers. Under the traditional approach, the analyst would naïvely conclude that anti-white bias exists, yielding an erroneous portrait of racial discrimination in the use of force.

Dean Knox, Will Lowe, Jonathan Mummolo

Looking only at data often give the wrong causal impression — especially when, as in this case, the data is loaded right from the start and results in sample selection bias due to post-treatment conditioning. Comparing white bank robbers to black civilians committing no crime does not give us the apples to apples comparison needed for making causal inferences.

Data — no matter if ‘big’ or not — never by itself give us credible causal inferences.


  1. Prof. Syll concludes that: “Looking only at data often gives the wrong causal impression”. This conclusion is deficient to the extent of being misleading and incorrect.
    Prof. Syll recognises that the problem in this case is “sample selection bias”.
    This bias is evident from additional data and information. How else could we possibly know about any such bias?
    To check for and if possible correct for such bias requires taking into account all relevant additional data/information, rather than naively using only partial or incomplete data.
    Unfortunately Prof. Syll does not mention this aspect of empirical work.
    Instead his conclusion seems to imply that we need an unspecified non-data source of knowledge.
    Perhaps he is still dreaming about the mysterious knowledge of “deep reality” which critical realist philosophers claim to possess.

    • Data alone can never solve any causal inference problems. Never. Statistics can give us correlations. We must have knowledge about mechanisms and processes to be able to draw causal conclusions. This is something all causality researchers agree on and has nothing at all to do with whether you’re a critical realist or not.

  2. https://www.svt.se/nyheter/lokalt/sormland/larm-om-flera-brander-i-eskilstuna

    What is the casual factor behind this? Put science to work?

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