&gt; A dramatic drop in violent crime since the 1970s because the &quot;self-appointed masterminds&quot; restricted lead<p>There are many possible factors that went into this reduction in crime, but it&#x27;s not entirely settled. For example, a substantial portion is attributable to a decrease in unwanted pregnancies [1].<p>1. <a href="http:&#x2F;&#x2F;pricetheory.uchicago.edu&#x2F;levitt&#x2F;Papers&#x2F;LevittUnderstandingWhyCrime2004.pdf" rel="nofollow">http:&#x2F;&#x2F;pricetheory.uchicago.edu&#x2F;levitt&#x2F;Papers&#x2F;LevittUndersta...</a>