Econometrica: Jan 1979, Volume 47, Issue 1

Sample Selection Bias as a Specification Error

https://doi.org/0012-9682(197901)47:1<153:SSBAAS>2.0.CO;2-J
p. 153-162

James J. Heckman

This paper discusses the bias that results from using nonrandomly selected samples to estimate behavioral relationships as an ordinary specification error or "omitted variables" bias. A simple consistent two stage estimator is considered that enables analysts to utilize simple regression methods to estimate behavioral functions by least squares methods. The asymptotic distribution of the estimator is derived.

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