Some methodological aspects of a retrospective follow-up study.
D002170:Canada; D004812:Epidemiologic Methods; D004813:Epidemiology; D005500:Follow-Up Studies; D006801:Humans; D007938:Leukemia / Q000209:etiology*; D008499:Medical Records; D011087:Polycythemia Vera / Q000150:complications*; D012106:Research; D012189:Retrospective Studies; D014481:United States