In a cohort breast cancer study, a woman is considered to be "exposed" if she first gave birth at age 30 or older. In a sample of 4540 women who gave birth to their first child before the age of 30, 65 developed breast cancer. Of the 1628 women who first gave birth at age 30 or older, 31 were diagnosed with breast cancer.
-Estimate the percentage of the disease among the exposed that is attributed to the exposure.

Question

Quizplus · Accepted Answer

The percentage of the disease among the exposed that is attributed to the exposure is calculated as (RR-1)*100, where RR is the relative risk. The relative risk is calculated as the incidence rate among the exposed divided by the incidence rate among the unexposed. The incidence rate among the exposed is 31/1628 = 0.0190 and the incidence rate among the unexposed is 65/4540 = 0.0143. Therefore, the relative risk is 0.0190/0.0143 = 1.33. The percentage of the disease among the exposed that is attributed to the exposure is (1.33-1)*100 = 25%.

In a Cohort Breast Cancer Study, a Woman Is Considered