The paper based the freakenomics study was based on only looked at US data but crime was dropping in the 90&#x27;s globally. A global drop in crime would be hard to explain based on US policy changes with regards to abortion while lead was removed globally at different times.<p><a href="http:&#x2F;&#x2F;www.bbc.com&#x2F;news&#x2F;magazine-27067615" rel="nofollow">http:&#x2F;&#x2F;www.bbc.com&#x2F;news&#x2F;magazine-27067615</a><p>The abortion hypothesis was also correlation study (i.e. These graphs look similar) but didn&#x27;t control for leaded gasoline. Also later studies failed to find more direct links such as higher rates of abortion in high crime areas that would explain the magnitude of the drop.<p>A later study by the author of the paper suggesting lead as the driver of violent crime did a follow up study that incorporated lead, abortion and other variables found that lead was the dominant contributor and abortion a secondary contributor.<p><a href="http:&#x2F;&#x2F;www.nber.org&#x2F;digest&#x2F;may08&#x2F;w13097.html" rel="nofollow">http:&#x2F;&#x2F;www.nber.org&#x2F;digest&#x2F;may08&#x2F;w13097.html</a>