Observational research methods—Cohort studies, cross sectional studies, and case–control studies

AbstractCohort, cross sectional, and case–control studies are collectively referred to as observational studies. Observational studies are often the only practicable method of answering questions of aetiology, the natural history and treatment of rare conditions and instances where a randomised controlled trial might be unethical.Cohort studies are used to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect. Cross sectional studies are used to determine prevalence. They are relatively quick and easy but do not permit distinction between cause and effect. Case controlled studies compare groups retrospectively. They seek to identify possible predictors of outcome and are useful for studying rare diseases or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies