Biostatistics and epidemiology
Cohort studies: prospective and retrospective
How cohort studies run forwards from exposure to outcome, the measures they yield (risk, rate, RR, attributable risk), prospective versus retrospective designs, and their strengths and weaknesses.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- A cohort study starts with people free of the outcome, classifies them by exposure, and counts new cases over time.
- It measures incidence directly, so it yields risk, rate, relative risk (RR), risk difference and hazard ratio.
- Prospective: the investigator enrols now and follows forwards. Retrospective (historical): exposure and outcome are reconstructed from records that already exist. Both run from exposure to outcome.
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Sources
- The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studiesLancet (von Elm et al., 2007;370:1453-7), 2007
- NHMRC additional levels of evidence and grades for recommendations for developers of guidelinesAU/NZNational Health and Medical Research Council, 2009
- Guidelines for Guidelines: assessing certainty of evidenceAU/NZNational Health and Medical Research Council, current
- Mortality in relation to smoking: 50 years' observations on male British doctorsBMJ (Doll, Peto, Boreham and Sutherland, 2004;328:1519), 2004
- Gordis Epidemiology (6th ed.)Elsevier (Celentano and Szklo, 2019), 2019
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy