Murder Is Down 63% in San Francisco. Lead Probably Isn't the Reason.

| Mon Jul. 7, 2014 7:21 PM EDT

Every time a city reports a big drop in crime, someone sends me a link to a story about it. San Francisco is the latest:

During the first half of the year, the city saw 14 killings — a 36 percent drop from the 22 recorded at the midpoint last year and a 63 percent decrease from the 38 in 2012.

...."The best guess one can make is that they're associated with a national trend of lowered homicide rates over the last 20 years," said Robert Weisberg, a law professor who co-directs the Stanford Criminal Justice Center. "They have settled a bit, but they have gone down in some places."

Weisberg said one big factor in the national drop in killings is "just smarter policing, which requires more police and smarter police, and that includes the use of technology, the targeting of hot spots and CompStat-style policing and gang intervention."

I know what you're wondering: is it lead, Kevin? What about this "smarter policing" stuff? Here are a few things that should help you think about this stuff:

  • The long-term trend in San Francisco is pretty familiar, and pretty similar to other mid-size cities. Over the past 20 years, a big part of San Francisco's drop in violent crime is probably due to the phaseout of leaded gasoline between 1975 and 1995.
  • However, lead isn't responsible for short-term changes. It has nothing to do with the 63 percent drop in homicides since 2012.
  • Generally speaking, you have to be careful with homicide numbers. Overall violent crime statistics are based on a large number of incidents, so they're fairly reliable. But even big cities don't have that many murders, which means the numbers can bounce around a lot from year to year just by random chance.
  • A drop in crime can create a virtuous circle, because it allows police to spend more time on the crime that remains. So lead might well have acted as a sort of tailwind here, producing a drop in violent crime that allowed systems like CompStat to be more effective, thus producing further drops even after the impact of lead has flattened out.

The phaseout of leaded gasoline did its job in San Francisco, but at this point any further drops will most likely have to come from other sources. More effective policing strategies are certainly one of the things that can make a difference.

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