Reproducibility of oral contraceptive histories and validity of hormone composition reported in a cohort of US women

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.