7.4 Covariates: Confounding/overcontrol bias

  • Example: Party identification → Vote choice (G. King 2010b)

  • Common-cause confounding bias

    • Q: Should we control for race (U.S. example). Why or why not?
      • idea: “use whatever information you have about why treatment and control [… ] [units] are not readily comparable and adjust for these differences statistically […] works well to the extent that you can figure out and measure the confounders and how they are related to treatment […] not good if you don’t know what the confounders are” (Egap)

  • Overcontrol/post-treatment bias

    • Q: Should we control for voting intentions measured five minutes before voting/vote choice?

  • See Keele (2015b), Elwert and Winship (2014a) and Montgomery and Nyhan (2016)

References

Elwert, Felix, and Christopher Winship. 2014a. “Endogenous Selection Bias: The Problem of Conditioning on a Collider Variable.” Annual Review of Sociology 40 (1): 31–53.

Keele, Luke. 2015b. “The Statistics of Causal Inference: A View from Political Methodology.” Polit. Anal. 23 (3): 313–35.

King, Gary. 2010b. “A Hard Unsolved Problem? Post-Treatment Bias in Big Social Science Questions.” In Hard Problems in Social Science” Symposium, Harvard University.

Montgomery, Jacob M, and Brendan Nyhan. 2016. “How Conditioning on Post-Treatment Variables Can Ruin Your Experiment and What to Do About It.”