Exchangeability in the case-crossover design

Int J Epidemiol. 2014 Oct;43(5):1645-55. doi: 10.1093/ije/dyu081. Epub 2014 Apr 22.


In cohort and case-control studies, confounding that arises as a result of differences in the distribution of determinants of the outcome between exposure groups leading to non-exchangeability are addressed by restriction, matching or with statistical models. In case-only studies, this issue is addressed by comparing each individual with his/herself. Although case-only designs use self-matching and only include individuals who develop the outcome of interest, issues of non-exchangeability are identical to those that arise in traditional case-control and cohort studies. In this review, we describe one type of case-only design, the case-crossover design, and discuss how the concept of exchangeability can be used to understand issues of confounding, carryover effects, period effects and selection bias in case-crossover studies.

Keywords: Epidemiology; case-crossover.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Case-Control Studies
  • Cohort Studies
  • Confounding Factors, Epidemiologic*
  • Cross-Over Studies
  • Humans
  • Research Design*
  • Selection Bias*