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Matching as Nonparametric Preprocessing for Reducing Model Dependence in Parametric Causal Inference

Published online by Cambridge University Press:  04 January 2017

Daniel E. Ho ,
Kosuke Imai ,
Gary King  and
Elizabeth A. Stuart
Daniel E. Ho
Affiliation:
Stanford Law School, 559 Nathan Abbott Way, Stanford, CA 94305. e-mail: [email protected]
Kosuke Imai
Affiliation:
Department of Politics, Princeton University, Princeton, NJ 08544. e-mail: [email protected]
Gary King
Affiliation:
Department of Government, Harvard University, 1737 Cambridge Street, Cambridge, MA 02138. e-mail: [email protected] (corresponding author)
Elizabeth A. Stuart
Affiliation:
Departments of Mental Health and Biostatistics, Johns Hopkins Bloomberg School of Public Health, 624 North Broadway, Room 804, Baltimore, MD 21205. e-mail: [email protected]
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Abstract

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Although published works rarely include causal estimates from more than a few model specifications, authors usually choose the presented estimates from numerous trial runs readers never see. Given the often large variation in estimates across choices of control variables, functional forms, and other modeling assumptions, how can researchers ensure that the few estimates presented are accurate or representative? How do readers know that publications are not merely demonstrations that it is possible to find a specification that fits the author's favorite hypothesis? And how do we evaluate or even define statistical properties like unbiasedness or mean squared error when no unique model or estimator even exists? Matching methods, which offer the promise of causal inference with fewer assumptions, constitute one possible way forward, but crucial results in this fast-growing methodological literature are often grossly misinterpreted. We explain how to avoid these misinterpretations and propose a unified approach that makes it possible for researchers to preprocess data with matching (such as with the easy-to-use software we offer) and then to apply the best parametric techniques they would have used anyway. This procedure makes parametric models produce more accurate and considerably less model-dependent causal inferences.

Type
Research Article
Information
Political Analysis , Volume 15 , Issue 3 , Summer 2007 , pp. 199 - 236
Copyright
Copyright © The Author 2007. Published by Oxford University Press on behalf of the Society for Political Methodology 

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