@article{ref1,
title="Frequency of anti-collision observing responses by solo pilots as a function of traffic density, ATC traffic warnings, and competing behavior",
journal="Aerospace medicine",
year="1973",
author="Lewis, M. F.",
volume="44",
number="9",
pages="1048-1050",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0001-9402",
doi="",
url="http://dx.doi.org/"
}