GPH 32: Cohort Studies

If case–control studies look backward from outcome to exposure, cohort studies begin with exposure and move forward in time to observe outcome.This chapter explores the structure and analytic power of cohort designs.A cohort study identifies groups based on exposure status and follows them prospectively - or retrospectively through existing records - to measure incidence of disease.Cohort studies are particularly valuable for:* Establishing temporal sequence* Calculating incidence directly* Studying multiple outcomes from a single exposure* Investigating rare exposuresKey methodological considerations include:* Selection of exposed and unexposed groups* Minimising loss to follow-up* Controlling confounding* Measuring exposure accurately* Calculating relative risk and attributable riskUnlike case–control studies, cohort designs allow direct estimation of risk and rate.Prospective cohorts offer precision and clarity but can be expensive and time-consuming. Retrospective cohorts leverage existing data but depend on data quality.The chapter also discusses classic long-term cohort studies that reshaped public health understanding of chronic disease risk.Cohort studies provide one of the strongest observational designs for causal inference - short of randomised trials.They allow epidemiology to observe disease emergence in real time.Key Takeaways* Cohort studies begin with exposure classification.* They allow direct calculation of incidence and relative risk.* Establish temporal relationship between exposure and outcome.* Useful for studying multiple outcomes.* Particularly suited for rare exposures.* Loss to follow-up threatens validity.* Prospective and retrospective designs differ in cost and control.* Strong observational evidence for causality. This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit drmanaankarray.substack.com/subscribe