@article{ref1,
title="Understanding Why Crime Fell in the 1990s: Four Factors That Explain the Decline and Six That Do Not",
journal="Journal of economic perspectives",
year="2004",
author="Levitt, Steven D.",
volume="18",
number="1",
pages="163-190",
abstract="<p>[Abstract unavailable]</p>",
language="",
issn="0895-3309",
doi="",
url="http://dx.doi.org/"
}