Oral contraceptive use: interview data versus pharmacy records.

Abstract

If women tend to forget and underreport their past oral contraceptive (OC) use, but the recall among cases is enhanced by the presence of disease, recall bias may explain some reported health effects of OC use. Two different sources of information on lifetime OC use were compared for 427 (84%) of a community-based sample of 511 women aged 20-34: (i) structured interviews, using a life event calendar and picture display as memory aids, and (ii) a register of all prescriptions dispensed by pharmacies in the county since 1970. Interview data and pharmacy records showed high levels of agreement for any OC use, current use, time since first and last use, total duration of use, and for duration of use in different 'time windows'. But there was a tendency to under-report specific kinds of OC used in the past. Underreporting of OC use among non-cases would usually introduce little or no bias (as compared to pharmacy records) for this kind of interview and women. However, it may be preferable to use interviews for current OC use, and pharmacy records for specific kinds of OC used in the past.