Question

The Family Planning Association in Oxford, England studied 17,000 women who had been enrolled in a cohort study between 1968 and 1974 to look at the association between oral contraceptive (OC) use and venous thromboembolism (Vessey et al., 1989). For current users of OCs, person-time was counted from the time a woman began using OCs. For never or past users, it was counted from the time a woman enrolled in the study. Woman-years were counted until venous thromboembolism occurred, the woman was lost-to-follow-up, or the end of the study.

a. The incidence rate of venous thromboembolism was 53 per 100,000 woman-years among current OC users and 6 per 100,000 woman-years among never or past users. Calculate the relative risk of venous thromboembolism for current users compared with never or past users. (1 point)

Answer 1

Answer: Number of current users = 53

Total number of individuals = 100,000

Number of past or never users = 6

Total number of individuals = 100,000

Therefore, the relative risk = (53/100,000)/ (6/100,000)

                                           = 53/6

                                           = 8.83

Thus, the relative risk is more in the exposed group in compared to the unexposed group.