Oral Contraceptives and Thromboembolic Disease

Richard Doll, MD, FRCP, FRS; Martin Vessey, MD
JAMA. 1972;220(3):417. doi:10.1001/jama.1972.03200030074027.
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To the Editor.—  The recent article by Drill1 covers much the same ground as an earlier paper by Drill and Calhoun,2 and to avoid reiteration we refer the reader to our comments on that earlier paper.3 One or two observations on the more recent article might, however, help the reader to judge its scientific value.In Table 3, Drill summarizes the findings in a number of large-scale clinical trials of oral contraceptives in which 63 cases of thromboembolism were recorded. According to Drill, 151 cases of thromboembolism would have been expected in these trials if the women taking part had experienced the "normal incidence" of the disease. Drill states that this difference is not statistically significant. This is clearly untrue. In fact, such a difference would occur by chance less than once in 1,000 times.In the study carried out by Inman and Vessey,4 26 deaths


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