Selection bias and misclassification in case-control studies conducted using the National Violent Death Reporting System.

Conducting case-control studies using the National Violent Death Reporting System (NVDRS) has the potential to introduce selection bias and misclassification through control selection. Some studies that use NVDRS compare groups of individuals who died by one mechanism, intent or circumstance, to individuals who died by another mechanism, intent or circumstance. For aetiological studies within NVDRS, the use of controls who had a different type of violent death has the potential to introduce selection bias, while relying on narrative summaries for exposure measurement may result in misclassification. We discuss these two methodological issues, and identify an unusual circumstance in which selection of live controls within NVDRS can be employed.