Case-control differences in the reliability of reporting a history of induced abortion.

The authors investigated the possibility that, in interview-based case-control studies, controls are more likely than cases to underreport a history of induced abortion. A case-control study was conducted in White women under 45 years of age who had given birth in Washington State during 1984-1994. The cases were women in three metropolitan counties of Washington State diagnosed with invasive breast cancer during 1984-1994; controls were selected through random digit dialing. A history of induced abortion among study participants was compared between interview data and information collected on the birth record of the last child to whom they gave birth (225 cases, 303 controls). Among women with a prior induced abortion recorded on the birth record, 14.0% of the 43 cases and 14.9% of the 47 controls did not report an induced abortion at interview (difference = -0.9%, 95% confidence interval of the difference: -15, 14). The authors' data do not suggest that controls are more reluctant to report a history of induced abortion than are women with breast cancer.