Histories of oral contraceptive (OC) use were reported by 116,686 women aged 25 to 42 years in the Nurses' Health Study II on a self-administered questionnaire accompanied by a color photo booklet of all OC preparations ever marketed in the US. To evaluate the quality of this information, we compared the responses of a randomly selected sample of 215 participants with their data from a subsequent, detailed telephone interview using a structured life events calendar. Agreement for a history of ever having used OC was high between the two methods (exact agreement 99%). Reported durations of use were equivalent (mean duration 42.7 months by telephone interview and 44.6 months by questionnaire). The Spearman correlation for duration of use calculated from the two methods was 0.94 (p < 0.0001). For a subset of women for whom we were able to obtain OC prescription records, the medical record confirmed the use of an identical or equivalent brand in 75% of intervals of reported use. Acceptably valid OC histories were obtained with a self-administered questionnaire.
PIP: Recall bias is a major concern in case-control studies of the association between oral contraceptives (OCs) and conditions such as breast cancer or thromboembolism. Studies of the validity of OC use histories have been limited, however, by the difficulty of obtaining reference information. The 116,686 US women 25-42 years of age enrolled in the self-administered Nurses' Health Study II were provided color photographs of all OCs ever marketed in the US for reference in providing their OC use histories. The quality of these responses was evaluated in telephone interviews conducted 6-14 months later with a randomly selected sample of 215 of these women who completed a structured reproductive life events calendar. There was 99% agreement between these two reporting methods for history of OC ever-use. Of 38 women who reported never using OCs in the telephone interview, only 1 had reported such use on the questionnaire. Reported durations of OC use also were equivalent (mean duration, 42.7 months by telephone interview and 44.6 months by questionnaire). In the subset of 150 women for whom OC prescription records were available, the medical record confirmed use of an identical or equivalent OC brand as identified in the questionnaire in 75% of intervals of reported use. Most disagreements were due to minor differences in dose; 90% matched on category of estrogen type and 74% matched on progestin type. These findings suggest that valid OC histories can be obtained through self-administered questionnaires and that the small amount of misclassification that occurs should not obscure important associations with disease.