MPD cruiser (file photo)

MPD cruiser (file photo)

The year 2012 ended with a notable statistic that was touted by both politicians and the media as a succes: the District, once known as the murder capital, had fewer than 100 homicides (88 to be exact).  City leaders, police officials, and residents hail it as a victory for Chief Lanier’s policing.  Over the past 20 years, violent crime has dropped to about half of what it was in 1992 in DC.  And, as it turns out, nationwide.  That’s correct- DC’s crime reduction follows a national crime trend, and isn’t very unique. 

The big question is: Why?  If effective policing, tougher prosecution, local policies, and politicians are hailed as key to the success, why are similar results seen nationwide?  Sure, some correlation with other major cities is to be expected, but what is a logical explanation for most cities’ crime stats  follow the same trend, even if policing, officials, and demographics differ?    Yes, reductions in violent crime are an achivement, but who (or what) deserves the credit?

The 1960-1980′s saw a nationwide uptick in crime, and many blamed it on socioecomic factors or drug epidemics and the resulting crimes supporting use and distribution.  New York City responded by electing Rudy Giuliani, who promised to get tough on crime and bought into the broken windows theory that if the police stepped up enforcement of smaller quality-of-life crimes (“broken windows”) that other crimes would reduce as well.  It seemed to work, with the late 1990′s showing declining crime in NYC.  However, an article in Mother Jones explores the topic a bit more, noting that the crime reductions aren’t unique:

Second, and far more puzzling, it’s not just New York that has seen a big drop in crime. In city after city, violent crime peaked in the early ’90s and then began a steady and spectacular decline. Washington, DC, didn’t have either Giuliani or Bratton, but its violent crime rate has dropped 58 percent since its peak. Dallas’ has fallen 70 percent. Newark: 74 percent. Los Angeles: 78 percent.

There must be more going on here than just a change in policing tactics in one city. But what?

Continuing on, the author of the Mother Jones piece posits that policing, elected officials, and the drug war don’t deserve all the credit.  Instead, there’s a strong link between the rise and fall of leaded gasoline in the 1940′s-1970′s and the rise and fall in crime 20 years later- notable since the youth of the 60′s and 70′s exposed to airborne lead from gasoline would have been the age group most responsible for crimes of the 1980′s and 90′s.  And, as it turns out, there’s a link between childhood lead exposure and juvenile delinquency- a researcher published in 1999 a study showing links between lead and violent crime:

 

A recent study had suggested a link between childhood lead exposure and juvenile delinquency later on. Maybe reducing lead exposure had an effect on violent crime too?

That tip took Nevin in a different direction. The biggest source of lead in the postwar era, it turns out, wasn’t paint. It was leaded gasoline. And if you chart the rise and fall of atmospheric lead caused by the rise and fall of leaded gasoline consumption, you get a pretty simple upside-down U: Lead emissions from tailpipes rose steadily from the early ’40s through the early ’70s, nearly quadrupling over that period. Then, as unleaded gasoline began to replace leaded gasoline, emissions plummeted.

 Gasoline lead may explain as much as 90 percent of the rise and fall of violent crime over the past half century.

Intriguingly, violent crime rates followed the same upside-down U pattern. The only thing different was the time period: Crime rates rose dramatically in the ’60s through the ’80s, and then began dropping steadily starting in the early ’90s. The two curves looked eerily identical, but were offset by about 20 years.

 

Now, of course, correlation doesn’t equal causation.  Looking further, one researcher found that crime rates closely mirrored use of leaded gasoline, even down to the city (and sometimes neighborhood) level:

In fact, use of leaded gasoline varied widely among states, and this gave Reyes the opening she needed. If childhood lead exposure really did produce criminal behavior in adults, you’d expect that in states where consumption of leaded gasoline declined slowly, crime would decline slowly too. Conversely, in states where it declined quickly, crime would decline quickly. And that’s exactly what she found.

As it turns out, similar patterns emerge not just at the neighborhood, city, state, and national levels, but internationally as well:

Nevin collected lead data and crime data for Australia and found a close match. Ditto for Canada. And Great Britain and Finland and France and Italy and New Zealand and West Germany. Every time, the two curves fit each other astonishingly well. When I spoke to Nevin about this, I asked him if he had ever found a country that didn’t fit the theory. “No,” he replied. “Not one.”

It’s certainly an interesting hypothesis, and something to think about considering the DC police department insists it needs more funding for more officers despite large reductions in crime- almost 60% lower violent crime over 20 years.   Meanwhile, crime analysis in DC is sorely lacking, where most blindly attribute crime reduction solely to unspecified strategies of police without considering other factors affecting crime.  Yes, police work is to be commended, but we must realize other factors- including poverty, parenting, education, and possibly lead- also affect crime.

The Mother Jones article  is well-written and provides much more detail on this issue, which admittedly needs more analysis and research.  However, it certainly provides a great example of crime analysis that considers other casues of crime (and crime reduction).