Unintended Consequences, Lead And Crime

from the the-world-works-in-bizarre-ways dept

If you haven't yet, you owe it to yourself to read Kevin Drum's recent article for Mother Jones about the possible link between crime rates and leaded gasoline. The article makes a rather convincing case that the massive growth, and then subsequent decline, in crime over the last six decades or so was influenced quite strongly by the fact that automobile gasoline had lead -- and then went unleaded due to environmental concerns. The article cites numerous studies that all seem to suggest the same thing -- and carefully tries to get past the "correlation is not causation" issue by looking at multiple studies that tackle the same question from different angles (different time periods, locations, population types, etc.) to try to eliminate other possible explanations. One of the parts that struck me as most interesting was the data on big cities as compared to other regions:

Like many good theories, the gasoline lead hypothesis helps explain some things we might not have realized even needed explaining. For example, murder rates have always been higher in big cities than in towns and small cities. We're so used to this that it seems unsurprising, but Nevin points out that it might actually have a surprising explanation—because big cities have lots of cars in a small area, they also had high densities of atmospheric lead during the postwar era. But as lead levels in gasoline decreased, the differences between big and small cities largely went away. And guess what? The difference in murder rates went away too. Today, homicide rates are similar in cities of all sizes. It may be that violent crime isn't an inevitable consequence of being a big city after all.

The article has not gone entirely without criticism. Drum has distanced himself from the claim of the key researcher he relies on in the piece that 90% of the rise and fall of crime (not 90% of crime) is attributable to lead, suggesting that 50% might be a more reasonable number. Separately, Ronald Bailey has reasonably taken Drum to task for blithely making statements about "blindingly obvious" things concerning IQ and ADHD that turn out to be... not true. When you take those things out of the equation, some of the report relies on "aggressiveness" and "impulsivity," but as Bailey notes, there is no national data series on aggressiveness or impulsivity. And, having seen way too many "studies" on video games / violent media causing greater "aggressiveness" and "impulsivity," but always failing to show that those traits actually lead to more crime, it pays to be somewhat skeptical.

That said, the data is very interesting, and certainly worth much more research and better understanding. At the very least, it's a reminder of our complex ecosystem and economy, where understanding cause and effect is often incredibly complicated, and the end results may be quite surprising. It is all too easy to jump to conclusions about cause and effect (and, yes, we are just as guilty of this as others at times) -- but the real world is an impossibly complex mixture of inputs and variables, that rarely succumb to simple explanations that follow the initial "most obvious" rationale.

Filed Under: crime, lead, statistics, unintended consequences