Abstract

Observational studies (OS) are clinical research designs whose goal is "the observation and description of events without any intervention in the natural course of these. Measurements can be made over the time (longitudinal study), either retrospectively or prospectively, or in a unique way (cross-sectional study). They can be used to report results in the areas of treatment and prevention, aetiology and harm, diagnosis, prognosis and natural history, scenarios in which OS give evidence of different levels, depending on the particular design and the area in question. As group of designs, OS represent the 70% to 80% of the publications of biomedical journals, independent of the database indexing and the eventual impact factor of each journal. The concept of OS includes case series, cross-sectional studies, population studies, and ecological and correlational studies; diagnostic tests studies, case-control studies and cohort studies.