FBI Director's Scary Murder Talk Ignores the Math

John Pfaff was quoted in a Bloomberg article about recent comments made by FBI Director James Comey, who has explained a rise in violent crime as a result of police concerns about being recorded while making arrests.

Critics, however, quickly pointed out that recent upticks in crime are being compared with historic lows. Fordham Law School professor John Pfaff noted on Thursday that percentage changes can be misleading:

2A. “Percent changes” hard to interpret: 10% change starting at 100 differs from 10% starting at 1000. Baserates: boring but critical!
[From John Pfaff’s Twitter feed]

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“It’s important to understand just how far murders have fallen since 1990,” Pfaff said. Gallup polls year after year find that people think crime is increasing, regardless of whether it is.

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Homicide trends also vary from place to place in America. In Chicago, one of the cities Comey singled out, the city recorded 196 murders through May 8, according to the city’s police statistics. This compares with 126 murders in the same period last year. While that’s a 56 percent increase, again, the percentage seems large because the base is low, compared to historic peaks. In 1991, Chicago had more than 900 homicides.

That doesn’t mean the numbers don’t warrant attention. But they also require context. “Do we sort of ignore this? No. But we shouldn’t be racing into [saying], ‘Oh my God, the crime drop is finally coming to an end,'” Pfaff said.

As for Comey’s suggestion that the numbers reflect changes in policing because of backlash to police shootings or fear of being caught on video, it’s too early to say. Scholars still debate the precise factors that contributed to the 1990s crime drop, after all. “Even if this is a sign of a trend, which we can’t say yet, understanding what’s causing that is probably years away,” Pfaff said.

Read the full piece.