Oral contraceptive use: interview data versus pharmacy records

Background If women tend to forget and underreport their past oral contrace ptive (OC) use, but the recall among cases is enhanced by the presence of d isease, recall bias may explain some reported health effects of OC use. Methods Two different sources of information on lifetime OC use were compar ed for 427 (84%) of a community-based sample of 511 women aged 20-34: (i) s tructured interviews, using a life event calendar and picture display as me mory aids, and (ii) a register of all prescriptions dispensed by pharmacies in the county since 1970. Results 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 underreport specific kinds of OC used in the past. Conclusion Underreporting of OC use among non-cases would usually introduce little or no bias (as compared to pharmacy records) for this kind of inter view 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.