retrospective study

1. a backward-looking review of the characteristics of a group of individuals in relation to morbidity, embracing some aspects of cross-sectional study and/or case control study. The term is sometimes loosely used as a synonym for such studies.

2. see cohort study.

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a longitudinal epidemiologic study in which participating individuals are classified as either having (cases) or lacking (controls) some outcome and their histories are examined for the presence of specific factors possibly associated with that outcome. Cases and controls are often matched with respect to certain demographic or other variables but need not be. As compared with prospective studies, retrospective studies suffer from drawbacks: although they can measure the odds ratio, which often approximates relative risk, they cannot reveal true incidence rates or attributable risk. Also, large biases can be introduced both in the selection of controls and in the recall of past exposure to risk factors. The advantage of the retrospective study is its small scale, usually short time for completion, and its applicability to rare diseases, which would require study of very large cohorts in prospective studies. See also prospective s.