In each of the past four years police nationwide have shot and killed almost the same number of people - nearly 1,000. Last year police shot and killed 998 people, 11 more than the 987 they fatally shot in 2017. In 2016, police killed 963 people, and 995 in 2015. Years of controversial police shootings, protests, heightened public awareness, local police reforms and increased officer training have had little effect on the annual total. The attention has not been enough to move the number. The Washington Post began tracking the shootings after Michael Brown, an unarmed black man, was killed in 2014 by police in Ferguson, Mo. A Post investigation found that the FBI's tracking system undercounted fatal police shootings by about half, because of the fact that reporting by police departments is voluntary and many departments fail to do so. In almost every case, a police shooting is an individual, unrelated event that can't be predicted. But because the data covers the entire United States and millions of police-civilian interactions ... statisticians can make predictions about the pattern of shootings, based only on knowing the overall number over four years. Then they can see if the prediction fits the observed pattern. With about 1,000 shootings each year, [statistician Sir David] Spiegelhalter said he would expect the number to range between around 940 and 1,060 annually, as long as no major systematic change occurs, like a dramatic reduction in crime rates.