@article{ref1,
title="'Why me?' versus 'why now?'--differences between operational hypotheses in case-control versus case-crossover studies",
journal="Pharmacoepidemiology and drug safety",
year="2007",
author="Maclure, M.",
volume="16",
number="8",
pages="850-853",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="1053-8569",
doi="10.1002/pds.1438",
url="http://dx.doi.org/10.1002/pds.1438"
}