title: Within-subject exposure dependency in case-crossover studies.
abstract: In the case-crossover design, only cases are sampled and the hazard ratio is estimated from within-subject comparisons of exposures at the event time and in M control periods prior to the event. We consider the effect of within-subject dependence of exposures in successive time periods. We show that estimates obtained from the conditional logistic model are biased. This bias disappears if the distribution of exposures in the M+1 successive time intervals is exchangeable. In contrast, the Mantel-Haenszel estimator for the odds ratio is approximately unbiased provided that exposures are stationary. Suitable methods of analysis of case-crossover designs using maximum likelihood may be derived from cohort rather than case-control models.
authors.affiliation: Department of Statistics, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K. s.k.vines@open.ac.uk
authors.forename: S K
authors.initials: SK
authors.lastname: Vines
authors.forename: C P
authors.initials: CP
authors.lastname: Farrington
mesh_terms: D015982:Bias; D016022:Case-Control Studies; D018592:Cross-Over Studies; D006801:Humans; D016013:Likelihood Functions; D016015:Logistic Models