@article{ref1,
title="Normative and descriptive analysis of preschool free play social interaction rates",
journal="Journal of pediatric psychology",
year="1981",
author="Greenwood, C. R. and Walker, H. Milnes and Todd, N. M. and Hops, Hyman",
volume="6",
number="4",
pages="343-367",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0146-8693",
doi="",
url="http://dx.doi.org/"
}