General concepts in biostatistics and clinical epidemiology: observational studies with case-control design

Case-control studies have been essential to the field of epidemiology and in public health research. In this design, data analysis is carried out from the outcome to the exposure, that is, retrospectively, as the association between exposure and outcome is studied between people who present a condition (cases) and those who do not (controls). They are thus very useful for studying infrequent conditions, or for those that involve a long latency period. There are different case selection methodologies, but the central aspect is the selection of controls. Data collection can be retrospective (obtained from clinical records) or prospective (applying data collection instruments to participants). Depending on the objective of the study, different types of case-control studies are available; however, all present a particular vulnerability to information bias and confounding, which can be controlled at the level of design and in the statistical analysis. This review addresses general theoretical concepts concerning case-control studies, including their historical development, methods for selecting participants, types of case-control studies, association measures, potential biases, as well as their advantages and disadvantages. Finally, concepts about the relevance on this study design are discussed, with a view to aid comprehension for undergraduate and graduate students of the health sciences. This is the third of a methodological series of articles on general concepts in biostatistics and clinical epidemiology developed by the Chair of Scientific Research Methodology at the School of Medicine, University of Valparaíso, Chile.