7.2.1 Observational Study Designs

Observational study designs include prospective and retrospective cohort studies, case-control studies, cross-sectional studies, case series and case reports, and can be broken down into the broad categories of analytical studies and descriptive studies. Generally, descriptive studies describe the occurrence/presence of an outcome or exposure, whereas analytical studies describe the relationship between the exposure and an outcome. Due to the nature of observational study designs compared with experimental designs, they are more at risk of the influence of confounding factors and different sources of bias that are unavoidable, which will be discussed further below. Similar to the MOOSE statement (Stroup, Berlin et al. 2000), reviewers should also refer to the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) statement, which is a checklist of items that need to be addressed in studies reporting on cohort, case-control, and cross sectional study designs and provides guidance on how to report observational research (von Elm, Altman et al. 2007).