On quantifying the magnitude of confounding

Holly Janes, Francesca Dominici, Scott Zeger

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


When estimating the association between an exposure and outcome, a simple approach to quantifying the amount of confounding by a factor, Z, is to compare estimates of the exposure-outcome association with and without adjustment for Z. This approach is widely believed to be problematic due to the nonlinearity of some exposure-effect measures. When the expected value of the outcome is modeled as a nonlinear function of the exposure, the adjusted and unadjusted exposure effects can differ even in the absence of confounding (Greenland, Robins, and Pearl, 1999); we call this the nonlinearity effect. In this paper, we propose a corrected measure of confounding that does not include the nonlinearity effect. The performances of the simple and corrected estimates of confounding are assessed in simulations and illustrated using a study of risk factors for low birth-weight infants. We conclude that the simple estimate of confounding is adequate or even preferred in settings where the nonlinearity effect is very small. In settings with a sizable nonlinearity effect, the corrected estimate of confounding has improved performance.

Original languageEnglish (US)
Pages (from-to)572-582
Number of pages11
Issue number3
StatePublished - Jul 2010


  • Collapsibility
  • Confounding
  • Odds ratio

ASJC Scopus subject areas

  • Medicine(all)


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