patientcohort

A patient cohort is a defined group of individuals who share specific characteristics and are tracked over time to observe health outcomes. In epidemiology and clinical research, cohorts are used to study disease incidence, natural history, prognosis, and the effects of exposures or treatments on health over time.

Cohorts can be prospective, enrolling participants and collecting data forward from a starting point, or retrospective (historical), using existing records to reconstruct past exposure and outcomes. They may be exposure cohorts (comparing those exposed to a factor with those not exposed) or disease cohorts (patients with a condition followed to observe outcomes).

Data for patient cohorts are gathered from electronic health records, clinical registries, biobanks, and participant surveys. Outcomes may include mortality, progression, treatment response, or adverse events. Analyses often report incidence or risk, using measures such as relative risk, risk difference, and time-to-event hazard ratios derived from Cox models.

Strengths of cohort studies include the ability to establish temporal sequence between exposure and outcome, the estimation of incidence, and the study of multiple outcomes. Limitations include susceptibility to confounding and biases, loss to follow-up, and higher cost and longer duration compared with other designs.

Prominent examples include long-running population and disease cohorts such as the Framingham Heart Study and the UK Biobank. Cohort research is distinct from case-control and cross-sectional studies and from randomized controlled trials, though it often informs clinical guidelines and risk prediction models.