Endogenous Selection Bias: The Problem of Conditioning on a Collider Variable

Posted: 3 Aug 2014

See all articles by Felix Elwert

Felix Elwert

University of Wisconsin - Madison - Department of Sociology

Christopher Winship

Harvard University - Department of Sociology; Harvard University - Harvard Kennedy School (HKS)

Date Written: July 2014

Abstract

Endogenous selection bias is a central problem for causal inference. Recognizing the problem, however, can be difficult in practice. This article introduces a purely graphical way of characterizing endogenous selection bias and of understanding its consequences ( HernĂ¡n et al. 2004 ). We use causal graphs (direct acyclic graphs, or DAGs) to highlight that endogenous selection bias stems from conditioning (e.g., controlling, stratifying, or selecting) on a so-called collider variable, i.e., a variable that is itself caused by two other variables, one that is (or is associated with) the treatment and another that is (or is associated with) the outcome. Endogenous selection bias can result from direct conditioning on the outcome variable, a post-outcome variable, a post-treatment variable, and even a pre-treatment variable. We highlight the difference between endogenous selection bias, common-cause confounding, and overcontrol bias and discuss numerous examples from social stratification, cultural sociology, social network analysis, political sociology, social demography, and the sociology of education.

Suggested Citation

Elwert, Felix and Winship, Christopher, Endogenous Selection Bias: The Problem of Conditioning on a Collider Variable (July 2014). Annual Review of Sociology, Vol. 40, pp. 31-53, 2014, Available at SSRN: https://ssrn.com/abstract=2475582 or http://dx.doi.org/10.1146/annurev-soc-071913-043455

Felix Elwert (Contact Author)

University of Wisconsin - Madison - Department of Sociology ( email )

Madison, WI 53706
United States

Christopher Winship

Harvard University - Department of Sociology ( email )

33 Kirkland Street
Cambridge, MA 02138
United States

Harvard University - Harvard Kennedy School (HKS) ( email )

79 John F. Kennedy Street
Cambridge, MA 02138
United States

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