Post 5: Cohort Study Design

The case-control study is frequently contrasted with another type of observational study, cohort studies, where exposed and unexposed subjects are observed until they develop an outcome of interest.    Often called longitudinal and prospective studies, researchers measure exposure variables before the occurrence of outcomes and compare the disease incidence between the exposed and unexposed cohorts after an extended period of time¹.  

Image 4: Schematic diagram of Cohort study design

By comparing the incidences of the diseases in two groups, cohort studies provide some evidence on the cause-effect relationship between the exposure and outcome as the exposure factor preceded the outcome².  Cohort study findings show the strength of an association so that the population attributable risk can be calculated³, that is, the degree to which the exposure in question is responsible for the amount of the disease in the population. 

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1  Dickinson K.  Ecological study [unpublished lecture notes]. Flinders university; notes provided at lecture 2015 February 20.

2  Akogbeng A.  Community child health, public health and epidemiology:Principles of evidence based medicine. Arch Dis Child. 2005; 90:837-840

3  Hill HA Kleinbaum DG.  Encyclopedia of Biostatistics: Bias in cohort studies. John Wiley and Sons; 2005