The lead crime hypothesis has some pretty compelling evidence, including a consistent time-lag for the effect that fits crime rates in a variety of countries and states as legislation went into effect: <a href="http:&#x2F;&#x2F;rationalwiki.org&#x2F;wiki&#x2F;Lead-crime_hypothesis" rel="nofollow">http:&#x2F;&#x2F;rationalwiki.org&#x2F;wiki&#x2F;Lead-crime_hypothesis</a>