Freakonomics misses something

Have meant for years to write this.

Freakonomics (Levitt & Dubner, 2005) famously argued that Roe v Wade was the most statistically likely explanation for the dramatic fall in U.S. crime during the 1990s.  The hypothesis was that, after the early 1970s, unwanted babies were less often born, resulting in fewer maladapted folks to commit crimes 20 years later.

This was clever, unexpected and interesting, and did fit the data better than the half dozen alternative explanations the book considered.  However, it did not explain the dramatic rise in crime during the 1960s and 1970s.

Here is an alternative explanation the book did not consider:  post-traumatic stress disorder among returning veterans.  PTSD is well known to be linked to crime and violent behavior.  War-caused PTSD is known to trigger episodes of violent behavior, and over 30% of tested prison populations have PTSD.  

Large numbers of US soldiers began returning from Vietnam in the mid-1960s, about the same time as crime rates dramatically rose.  The rise in crime leveled off a few years after the US withdrew from Vietnam, and began to decline precipitously as the US veteran population aged.

Interestingly, the violent crime rate continued to fall until just a couple of years ago, when it turned back up again — coincidentally, just as large numbers of vets began to return from Iraq.

This idea leaves out a few things — for example, it does not explain why crime rates would not dramatically rise after WWII or Korea.  But for completeness, Levitt and Dubner should cover it.

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