Oral Contraceptives and Thromboembolic Disease

To the Editor.— The questions and comments made by several correspondents (220:416,1972) relative to our recent publications¹,²on oral contraceptives and thromboembolic disease may be answered briefly, as follows: The overall association of risk of hospital admission calculated by Dr. Sartwell from his pooled data is given on page 586.1 My further comments relative to the significance or lack of significance of hospital admission risk for individual cities or for specific diagnostic classifications are based on the individual statistical calculations given in Table 9 of his paper. The comment on studies involving between 1,000 and 2,000 womanyears of experience is of interest, but the incidence of 2.3±0.4 is not above the normal incidence for thromboembolic disease. If the premise had been examined further, it would have been noted that it is not supported by studies involving less than 1,000 woman-years of experience; in 53 such studies the