@article{ref1,
title="Three difficulties in the comparison of accident rates",
journal="Accident analysis and prevention",
year="1969",
author="Pfundt, K",
volume="1",
number="3",
pages="253-259",
abstract="<p>[Abstract unavailable]</p>",
language="en",
issn="0001-4575",
doi="",
url="http://dx.doi.org/"
}