Health registries as research tools: a review of methodological key issues.

Health registries provide opportunities for conducting large-scale, population-based studies, but attention must be devoted to their specific limitations. Herein, we describe potential limitations that may affect the validity of registry-based research. Our review includes descriptions of 1) populations, 2) variables, 3) medical coding systems for medical information and 4) selected key methodological challenges. Knowledge of such factors and epidemiological study designs in general is likely to increase the quality of registry-based research and reduce potential biases.