Appending epidemiological studies to conventional case-control studies (hybride case-control studies).

This paper summarizes several studies that can be appended to conventional case-control studies especially in the context of case-control studies that focus on etiologic questions. Appending studies to case-control studies may further add to the understanding of the epidemiology of diseases under investigation. We explain their uses, implications and limitations. One can append the following studies to a case-control study: (1) case-only study, (2) case crossover study, (3) case cross-sectional study, (4) control cross-sectional study, (5) case follow-up study, and (6) control follow-up study. The choice of the additional studies that are appended to the conventional case-control study has implications for the set of data and biological material that has to be collected, the ethical review board and the informed consent. Due to several limitations, the attachment of additional studies to a case-control study should be carefully considered and limited to only few additional studies in order to avoid overburden of the study participants and study personnel.