@article{ref1,
title="Clusters: who, what, where, how?",
journal="Prehospital and disaster medicine",
year="2010",
author="Birnbaum, Marvin L.",
volume="25",
number="5",
pages="385-386",
abstract="<p>[Abstract unavailable]</p> <p>Language: en</p>",
language="en",
issn="1049-023X",
doi="",
url="http://dx.doi.org/"
}