"Electing a black mayor leads to more black police officers"

Electing a black mayor leads to more black police officers

by Dan Hopkins at fivethirtyeight

http://fivethirtyeight.com/datalab/electing-a-black-mayor-leads-to-more-black-police-officers/

"SNIP...........................

At first glance, this data would seem to have the problem I brought up earlier: Correlation doesn’t equal causation. But in this case, we can get leverage from a basic fact about electoral math, which is that a candidate who wins 50.1 percent of the vote gets to be mayor and a candidate who wins 49.9 percent of the vote does not. On average, the cities where black candidates narrowly win should be similar to those where they narrowly lose — and the candidates should be similar, too. But a few chance votes either way put some candidates in City Hall and others into another line of work.

Following that logic, we can isolate the effect of narrowly being elected mayor as distinct from the effect of cities where black mayors win more support. In the figure below, from our paper, we plot the change in the share of the police force that is black over the three years post-election (on the y-axis) as the support for the black candidate in a given mayoral election changes (the x-axis). Each black diamond represents one election. The key change to notice is the upward shift just after the 50 percent mark, when the black candidate wins and can influence police hiring.



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Based on the model, a city where the black candidate wins one vote more than 50 percent should expect to see its share of black police officers jump by 3.8 percentage points. (The associated 95 percent confidence interval spans from 0.7 to 6.9). That’s the discontinuity illustrated by the break in the lines with black circles at 50 percent. And even if we drop Cincinnati as an outlier, the estimated effect of a narrow victory by the black candidate is still 2.2 percentage points, as the line defined by gray triangles demonstrates. (Incidentally, that is quite close to the change we’d see in Ferguson with the hiring of one new black officer.)

Of course, there is variation in police hiring across cities, with some black mayors presiding over declining shares of black officers and some non-black mayors overseeing increases. But overall, cities with black mayors appear to hire black officers in a way that other cities do not. It’s not just that blacks are too frequently underrepresented in city halls and police departments. It’s that underrepresentation in the halls of power leads to underrepresentation on the beat



..........................SNIP"