Via Kevin Drum:
Kevin’s longer piece on the crime-lead connection appears in Mother Jones (ungated and I haven’t read it yet). Coincidentally, Harold Pollack recently pointed me to this 2004 Steve Levitt paper (ungated PDF) on why crime fell in the 1990s. I haven’t read it yet either, but a quick search found this footnote:
Reyes (2002) offers an additional intriguing explanation for the decline in crime: the reduction in levels of lead in the blood due to the elimination of leaded gasoline and lead-based paints. Because of the highly speculative nature of the Reyes conjecture at the present time, I do not discuss this hypothesis at greater length, although it is clearly an area worthy of continued future research.
Also coincidentally, the recent Econtalk episode was on the prison population, but it also touches on changes in the crime rate.
PS: My previous chart of the day on health care spending by age and country turns out to be highly misleading. Go read the comments to see why if you haven’t yet. Kevin and Arnold Kling point to other problems.