Cohort study

A cohort study is an observational study in which groups of participants are selected based on whether they have been (or will be) exposed to a specific factor. These cohorts are then followed over time to determine if the exposure is associated with the development of a particular health outcome. Cohort studies can be prospective, where participants are recruited at the point of exposure and followed forward in time to observe outcomes, or retrospective, where existing data (such as registries) are used to identify exposed and unexposed groups and outcomes that have already occurred. While typically observational, cohort studies can also be interventional, where groups are defined by the treatments they receive as part of their routine care, allowing for the comparison of different interventions or dosages.