@article{ref1,
title="Certification in occupctional health: philosophy, implication, and mechanism. 4",
journal="American journal of public health",
year="1966",
author="Purdom, PW",
volume="56",
number="7",
pages="1130-1135",
abstract="<p>[Abstract unavailable]</p>",
language="",
issn="0090-0036",
doi="",
url="http://dx.doi.org/"
}