Population-Based Study

Abstract

Population-based studies aim to answer research questions for defined populations. Answers should be generalizable to the whole population addressed in the study hypothesis, not only to the individuals included in the study. This point addresses the point of external validity of the findings. Therefore, the valid definition as well as the reliable and valid identification of populations in which research questions for specific populations can be studied is the most important issue in population-based studies. Population-based studies may include a variety of study types. They may include case–control studies, cross-sectional studies, twin studies, or prospective and retrospective cohort studies. The important issue is the selection of the individuals that are included into the study – they should be representative of all individuals in the a priori defined specific population. For example, in a population-based prospective cohort study, in which an association between a specific exposure and a specific outcome (i.e., the onset of a certain disease) is studied, all individuals sampled for the study should be representative for the addressed population. This means that the individuals under exposure and non-exposure should be identified within the same population. They should differ only on the exposition factor. Likewise, in a population-based case–control study, cases and controls should be also identified in the same population. Otherwise, differences between cases and controls can be attributed to different population characteristics.