In the US all kinds of statistics are meticulously recorded on the basis of race or ethnicity. This kind of data is a luxury not easily afforded in many European countries, where we have endless debates about whether some ethnic group or other might be more prone to violent crime. In the US it is well known that African-Americans are roughly three-fold overrepresented in violent crime. This means that in US cities, the rate of violent crime is mostly determined by the percentage of the black population.
So in the US, instead, the debate can, though equally fruitlessly, cover the topic of possible causes and what best to do about them. One of these causes, eagerly championed by Steve Sailer, is the so called Ferguson effect. In the aftermath of black-lives-matter protests, crime rates allegedly spike, because the police walks back on discriminating but effective measure like racial profiling in frisk-and-stop.
Together with the Jussie Smollet case, this lead me to wonder whether black governance had an effect on black crime. If your key voters would punish you for the most effective measures against black crime, maybe you wouldn’t be so eager to implement these. Or maybe for a black mayor crime in the black community is a bigger priority and insights into how to alleviate the problem are more common?
So I created a list of cities with their general and specific violent crime rates, as well as their black percentage  and cross-bred it with a list of black mayors . Then I plotted black percentage against crime with every red dot a city with a black mayor and every blue dot a city without a black mayor. I am not sure how accurate and up to date these data is. And I am sure this analysis could be done in a much more principled way, but as a first look into the topic this gives already gives a clear tendency.
The correlation of black percentage and rape is much less tight than the other correlations. Would be interesting whether this is real or a result of more unreported cases.
Overall we see that cities with black mayor have less violent crime than other cities with the same black percentage. This trend is observable for all types of crime. And though there is a lot to be desired in our methodology, it seems unlikely that a more thorough investigation would yield the opposite result.
 Crime rate by city
 Black mayors