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TESTING LIMITED OVERLAP

Published online by Cambridge University Press:  13 May 2024

Xinwei Ma
Affiliation:
University of California, San Diego
Yuya Sasaki*
Affiliation:
Vanderbilt University
Yulong Wang
Affiliation:
Syracuse University
*
Address correspondence to Yuya Sasaki, Department of Economics, Vanderbilt University, 415 Calhoun Hall, Nashville, TN 37240, USA; e-mail: yuya.sasaki@vanderbilt.edu.
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Abstract

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Extreme propensity scores arise in observational studies when treated and control units have very different characteristics. This is commonly referred to as limited overlap. In this paper, we propose a formal statistical test that helps assess the degree of limited overlap. Rejecting the null hypothesis in our test indicates either no or very mild degree of limited overlap and hence reassures that standard treatment effect estimators will be well behaved. One distinguishing feature of our test is that it only requires the use of a few extreme propensity scores, which is in stark contrast to other methods that require consistent estimates of some tail index. Without the need to extrapolate using observations far away from the tail, our procedure is expected to exhibit excellent size properties, a result that is also borne out in our simulation study.

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Type
ARTICLES
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s), 2024. Published by Cambridge University Press