There’s long been a fierce debate about the effect of Black Lives Matter protests on the lethal use of force by police. A new study, one of the first to make a rigorous academic attempt to answer that question, found that the protests have had a notable impact on police killings. For every 4,000 people who participated in a Black Lives Matter protest between 2014 and 2019, police killed one less person. Travis Campbell, a PhD student in economics at the University of Massachusetts Amherst, released his preliminary findings on the Social Science Research network as a preprint, meaning the...