A Crash Course in Good and Bad Controls

27 Pages Posted: 29 Oct 2020 Last revised: 24 Jul 2021

See all articles by Carlos Cinelli

Carlos Cinelli

University of Washington - Department of Statistics

Andrew Forney

Loyola Marymount University

Judea Pearl

University of California, Los Angeles (UCLA) - Computer Science Department

Date Written: September 9, 2020

Abstract

Many students, especially in econometrics, express frustration with the way a problem known as “bad control” is evaded, if not mishandled, in the traditional literature. The problem arises when the addition of a variable to a regression equation produces an unintended discrepancy between the regression coefficient and the effect that the coefficient is expected to represent. Avoiding such discrepancies presents a challenge not only to practitioners of econometrics, but to all analysts in the data intensive sciences. This note describes graphical tools for understanding, visualizing, and resolving the problem through a series of illustrative examples. We have found that the examples presented here can serve as a powerful instructional device to supplement formal discussions of the problem. By making this “crash course” accessible to instructors and practitioners, we hope to avail these tools to a broader community of scientists concerned with the causal interpretation of regression models.

Keywords: Bad Control, Regression, Causal Inference, Omitted Variable Bias

JEL Classification: C01, C21

Suggested Citation

Cinelli, Carlos and Forney, Andrew and Pearl, Judea, A Crash Course in Good and Bad Controls (September 9, 2020). Available at SSRN: https://ssrn.com/abstract=3689437 or http://dx.doi.org/10.2139/ssrn.3689437

Carlos Cinelli (Contact Author)

University of Washington - Department of Statistics ( email )

Seattle, WA
United States

HOME PAGE: http://carloscinelli.com

Andrew Forney

Loyola Marymount University

7900 Loyola Boulevard
Los Angeles, CA 90045
United States

Judea Pearl

University of California, Los Angeles (UCLA) - Computer Science Department ( email )

4732 Boelter Hall
Los Angeles, CA 90095
United States

HOME PAGE: http://www.cs.ucla.edu/~judea/

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