Given the enthusiasm (perhaps out of social conformity pressure) many EAs had for the BLM movement last summer, I think we might perhaps consider this a cautionary tale:
From 2014 to 2019, Campbell tracked more than 1,600 BLM protests across the country, largely in bigger cities, with nearly 350,000 protesters. His main finding is a 15 to 20 percent reduction in lethal use of force by police officers — roughly 300 fewer police homicides — in census places that saw BLM protests.
Campbell’s research also indicates that these protests correlate with a 10 percent increase in murders in the areas that saw BLM protests. That means from 2014 to 2019, there were somewhere between 1,000 and 6,000 more homicides than would have been expected if places with protests were on the same trend as places that did not have protests. Campbell’s research does not include the effects of last summer’s historic wave of protests because researchers do not yet have all the relevant data.
The two theories he suggests are:
- BLM protests make people distrust the police, so they are less likely to dial 911, and less likely to cooperate with investigations.
- BLM protests change the cost-benefit for police, because they face additional risk of vilification/prosecution for intervening, so they spend more time protecting the doughnut shop and less time in dangerous neighborhoods.
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I disagree - the point estimate for the increase in murders is well above 0 for the entire time period [figure 6]. The effect possibly fades away a little over time, so the confidence interval extends slightly over zero, but that doesn't mean you can assume it is zero! If you did a statistical test for 'did the increase in killings reduce over time' you would not get a significant result.