Selection bias in the assessment of gene-environment interaction in case-control studies.

Selection bias is a common concern in epidemiologic studies, particularly case-control studies. Selection bias in the odds ratio occurs when participation depends jointly on exposure and disease status. General results for understanding when selection bias may affect studies involving gene-environment interactions have not yet been developed. In this paper, the authors show that the assessment of gene-environment interactions will not be subject to selection bias under the assumption that genotype does not influence participation conditional on exposure and disease status. This is true even when selection, including self-selection of subjects, is jointly influenced by exposure and disease and regardless of whether the genotype is related to exposure, disease, or both. The authors present an example to illustrate this concept.