ORAL CONTRACEPTIVES AND THROMBOEMBOLISM: A FURTHER REPORT1

Abstract

Sartwell, P. E. (Johns Hopkins Univ. School of Hygiene & Public Health, Baltimore, Md. 21205). Oral contraceptives and thromboembolism: a further report.Amer J Epidem 94: 92–201, 1971.—Additional findings from a case-control study of thromboembolism and oral contraceptives are presented. There was some association of smoking with recent use of orals, but no evidence that smoking enhanced their effect in producing clotting. Data on frequency of use of all contraceptive methods by cases and controls, according to age and religion, are presented. No evidence was found that other drugs taken by subjects enhanced the risk of thromboembolism. Some problems in the design of such studies are discussed. A probable difference in the use of oral contraceptives between those subjects who were interviewed and those who were not is shown. It is demonstrated that matching on factors associated with the dependent variable can produce a spurious decrease in relative risk when the data are pooled.