@article{ref1,
title="Drug use: association vs causation",
journal="Journal of Occupational Medicine",
year="1993",
author="Ryan, J. and Zwerling, Craig S. and Jones, Marc",
volume="35",
number="10",
pages="984-984",
abstract="Abstract unavailable.",
language="",
issn="0096-1736",
doi="",
url="http://dx.doi.org/"
}