Assessment of exposure misclassification bias in case-control studies using validation data.

It has recently been shown that the bias due to misclassification of a binary exposure in case-control studies can be simply expressed in terms of so-called quality indices. Quality indices are measures of the degree of misclassification that are symmetric with respect to the true and measured exposure. They can be estimated from sub-study validation data and used to estimate the bias. Bias is not present if quality indices are nondifferential with respect to cases and controls. In this article the sampling distribution of these indices is investigated by developing formulae for their standard errors and these formulae are used to derive the standard error of the estimated bias. Simulation studies are used to confirm the validity of the formulae. The formulae are used to assess the bias in two studies of risk factors for Sudden Infant Death Syndrome (SIDS) and can be applied to the assessment of diagnostic tests.