@article{ref1,
title="Equivalence formation by retarded and nonretarded children at different mental ages",
journal="American journal of mental deficiency",
year="1972",
author="Stephens, W. E.",
volume="77",
number="3",
pages="311-313",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0002-9351",
doi="",
url="http://dx.doi.org/"
}