An Editorial Viewpoint

To the Editor:—  Drill and Calhoun claim a lack of association between the administration of oral contraceptives and the occurrence of thromboembolic disease. The critical reply to this article by Doll, Inman, and Vessey serves to highlight the opposing views of the English studies. The fundamental differences in study designs employed in the English and American investigation may account for the different results obtained.The English study is a matched case/control study. It is based on the comparison of oral contraceptive usage in young married women hospital patients with thromboembolic disease with that of a nonthromboembolic control series from the same hospitals, carefully matched for age, parity, date of admission, and absence of any predisposing cause for thromboembolic disease. The reliability of the data appears to be high with respect to disease diagnosis, and the affected sample was representative of a substantial segment of the English population.In contrast, the