How does a cohort study differ from case-control studies?

A cohort study differs from case-control studies primarily in its design and the approach to measuring outcomes. In a cohort study, researchers start with a group of individuals (the cohort) who are initially free from the outcome of interest. They follow this group over time to observe who develops the outcome. This forward-looking approach allows researchers to measure how exposure to certain risk factors influences the likelihood of developing the outcome.

In contrast, case-control studies begin with individuals who already have the outcome of interest (the cases) and compare them to individuals without the outcome (the controls). Researchers then look backward to ascertain exposures, essentially identifying what risk factors may have contributed to the cases' condition.

This fundamental difference in directionality—moving forward in time for cohort studies versus looking back for case-control studies—is what distinguishes the two methodologies.