09-07-2009, 02:31 AM
. A cohort study is conducted to assess the relationship between oral contraceptive use and the risk of breast cancer. Participants are chosen from a closed-panel health
maintenance organization (HMO] and include 530 women between 30 and 40 years of age with no gynecologic disease. Each participant is asked to complete a
questionnaire about her use of an oral contraceptive. Twenty years later. 40% ofthe participants are enrolled in the same HMO. Of the 100 women who remained with the
HMO and continued to use an oral contraceptive. 12 patients had developed histologically confirmed breast cancer compared with 4 patients among the women who did not
use an oral contraceptive. Which ofthe following features of this study is most likely to affect its validity?
O A) Differential follow-up
O B) Lead time bias
O C) Misclassification of exposure
O D) Misclassification of outcome
O E) Recall bias