To the Editor.—
The recent article by Ralph I. Horwitz, MD, and Alvan R. Feinstein, MD, "Improved Observational Method for Studying Therapeutic Efficacy" (1981;246:2455), and accompanying editorials (1981;246:2481, 2482) imply that selection of cases and controls from within what was originally set up as a closed cohort is a novel and innovative epidemiologic method. This may be true for clinical trials, but case-control studies within cohorts are not unusual in epidemiologic research on industrial populations.1,2The cohort from which Drs Horwitz and Feinstein selected both cases and controls was described as part of a "large observational study" of patients hospitalized with myocardial infarction. Industrial cohorts usually consist of employees in a manufacturing facility.3 Drs Horwitz and Feinstein used lidocaine therapy as the independent variable for calculating odds ratios. Their dependent variable was death. In industrial case-control studies, the independent variable may be exposure to a chemical or a
Van Peenen PFD. Alternative Strategies to Randomized Clinical Trials. JAMA. 1982;247(15):2100. doi:10.1001/jama.1982.03320400020023
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