@article{ref1,
title="Nested case-control studies",
journal="BMJ",
year="2010",
author="Sedgwick, Philip",
volume="340",
number="",
pages="c2582-c2582",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0959-535X",
doi="10.1136/bmj.c2582",
url="http://dx.doi.org/10.1136/bmj.c2582"
}