Overview of study design in clinical epidemiology

Abstract

The range of clinical and epidemiological studies in sexual health is very wide, but in terms of purpose and basic study design, they can be divided into a few broad categories. The purpose may be to determine the level (prevalence) of disease in a population, to identify causes of disease or those at high risk of disease, to describe the natural history of disease, to prevent the onset of disease or alter the course of disease in individuals or populations. The simplest categorisation in terms of study design is between observational studies and intervention studies (trials). Observational studies, in which one observes the course of a disease or the relation between risk factors (exposures) and outcomes, are used to address questions about prevalence, natural history, aetiology, and risk groups. Trials, in which one intervenes to prevent or change the course of a disease, are used to evaluate preventive or therapeutic interventions, but can also provide strong evidence of causality (table 2).