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Monday, December 28, 2015

A Large Increase in Murders

At The Wall Street Journal, Heather MacDonald rebuts those who minimize the recent increase in violent crime.
The Brennan researchers gathered homicide data from 25 of the nation’s 30 largest cities for the period Jan. 1, 2015, to Oct. 1, 2015. ... The resulting projected increase for homicides in 2015 in those 25 cities is 11%. (By point of comparison, the FiveThirtyEight data blog looked at the 60 largest cities and found a 16% increase in homicides by September 2015.) An 11% one-year increase in any crime category is massive; an equivalent decrease in homicides would be greeted with high-fives by politicians and police chiefs. Yet the media have tried to repackage that 11% homicide increase as trivial.
Several strategies are employed to play down the jump in homicides. The simplest is to hide the actual figure. An Atlantic magazine article in November, “Debunking the Ferguson Effect,” reports: “Based on their data,the Brennan Center projects that homicides will rise slightly overall from 2014 to 2015.” A reader could be forgiven for thinking that “slightly” means an increase of, say, 2%. Nothing in the Atlantic write-up disabuses the reader of that mistaken impression.

A second strategy for brushing off the homicide surge is to contextualize it over a long period. Because homicides haven’t returned to their appalling early 1990s or early 2000s levels, the current crime increase is insignificant, the Brennan Center and its media supporters suggest, echoing an argument that arose immediately after I first documented the Ferguson effect nationally. ...” True enough, though irrelevant—good policing over the past two decades produced an extraordinary 50% drop in crime. America isn’t going to give all that back in one year. The relevant question: What is the current trend? If this year’s homicide and shooting outbreak continues, those 1990s violent crime levels will return sooner than anyone could have imagined.

The most desperate tactic for discounting the homicide increase is to disaggregate the average. “Fears of ‘a new nationwide crime wave’ are premature at best and wildly misleading at worst,” asserts the Atlantic, because the “numbers make clear that violent crime is up in some major U.S. cities and down in others.”

But such variance is inherent in any average. If there weren’t variation across the members of a set, no average would be needed.