2. Appraising the relevance of results

2.3 The eight steps

2. What is the study design?

With the exclusion of especially interesting or unusual cases, or a series of cases, there are four broad types of study designs:

  • Cross-sectional study: assesses the prevalence of a disease, its risk factors, and its other characteristics in a given population at a determined point of time.
  • Case-control study : an retrospective observational study, in which the characteristics of patients who have a disease (the cases) are compared with those of patients who do not have the disease (the controls).
  • Cohort study :an prospective observational study, in which a group of subjects exposed to the risk factors of a disease, is followed over a set period of time. The prevalence rate of the disease in the exposed group is compared to that of another group, not exposed the same risk factors, followed during the same time period.