Cohort study

From RationalWiki

A cohort study is a type of study that gathers data by observation. A typical study design would involve enrolling a large group of people and watching them for the appearance of a disease or other event of interest. This is less powerful than a randomized controlled trial, but allows examination of evidence that RCT's cannot evaluate.

Cohort studies are often contrasted to case-control studies. For example, if you are interested in the association between condom use and syphilis transmission, you could use a case-control design or a cohort design.

In the case-control design, you would look at people who have syphilis, and those who do not, and look at the rates of condom use in each group.

By contrast, in a cohort study, you would observe a group of people, recording who uses condoms and who does not, and looking at who catches syphilis and who does not, using statistics to calculate the strength of the relationship.

Theoretically, an RCT could be designed to look at the same question, but this would be unethical. The corresponding RCT would randomly assign a group of people to use condoms, and a similar group of people to not use condoms, and then let them do what they will, and calculate syphilis rates at the end.