Vox's Sarah Kliff offered six reasons for the fall in teen pregnancy rates earlier this year, but new research by Jessica Wolpaw Reyes from Amherst suggests a seventh: fewer children having their brains poisoned by exposure to lead. The suggestion that lead contamination is an important driver of crime rates has gained currency over the past several years (Kevin Drum is a particularly dogged and persuasive advocate of this view), and the point of Reyes' research is to look at a broader range of social problems among youth.
What she does is take advantage of the fact that leaded gasoline was phased out unevenly across states in the late-1970s and early-1980s to generate some not-quite-experimental data. You can see the results here:
Similar results are found for related "risky" behaviors such as the odds of having sex and drinking at an early age.
It's worth reflecting on the ways in which the political system is rigged to congenitally under-regulate these kind of health hazards. If you, as a politician, take a stand that goes against the financial interests of some group of incumbent industries your reward is that significant social ills are alleviated … 15 to 20 years after your proposal is phased into place. No governor or president — and very few senior legislators — sticks around long enough to claim credit for these things.
Nowadays the leaded gasoline problem is behind us, but there's still a lot more that could be done in terms of public efforts to clean up lead-contaminated soil, replace old lead pipes, and eliminate lead-based paint from old houses. But that would take money up front for a long-term payoff.