RESUMO
Case-control studies examining the effects of oral contraceptives (OC) are prone to misclassification bias due to errors in assessment of OC use. Concern about inaccurate exposure histories has increased since current studies require women to recall OC use over prolonged periods of time. In preparation for a case-control study of breast cancer and OC use, an investigation was carried out to assess agreement between women's lifetime histories of OC use (covering a period of up to 20 years) and prescribers' records. OC histories were obtained during personal interview with 218 women who had used OC at some point in their lives (127 breast cancer patients, 91 controls). Recall was aided by an album with color photographs of all OC marketed in the Netherlands from 1962 onwards (n = 65), and a calendar that covered the women's life span from date of birth to menopause. The participants were asked for the names of all physicians who prescribed OC for them. The rate of response from the prescribers was high (94%), but only half of the forms provided useful information. Patient-prescriber agreement on brand names (including dosage) was 70%. About half of the women agreed with their prescribers on starting dates to within less than a year's difference. Approximately the same percentage of agreement was found for stopping dates. Multiple linear regression indicated that agreement on brand names and dates of usage was lower for women of low socioeconomic status, for healthy women (as compared to breast cancer patients) and for periods of pill use that had to be recalled from the more distant past. Agreement on total duration of use was high enough to permit testing of a moderately strong duration-response relationship in a case-control study.
PIP: Between January 1983-January 1986, women spoke to 151 breast cancer patients at the National Cancer Institute in Amsterdam, the Netherlands and 93 healthy controls to determine agreement between women's lifetime histories of oral contraceptive (OC) use and prescribers' records. Both cases and controls provided the name of all physicians who ever prescribed an OC to them. Even though 93.6% of prescribers responded to the researchers request for information, only 46.1% of the forms provided information on brand name or date(s) of usage. In fact, only 33.6% had complete information. Median duration of OC use was 8.1 years and 33.1% began taking OCs before July 1965. Patient-prescriber agreement on brand names and dosage stood at 70%. Responses of starting dates of about 50% of the women corresponded within 1 year with that of their prescriber. Breast cancer patients tended to have better agreement than controls, but the difference was not significant. Further 59.1% agreed with their prescriber within 2 years on duration of use. The difference in agreement on duration of OC use between cases and controls was insignificant. The multiple regression analysis showed that women of low socioeconomic status were less likely to agree with their prescribers on brand names and dates of usage than were women of medium and high socioeconomic status. Further healthy women had better agreement than breast cancer patients. Moreover the recall period had a significant effect on agreement on brand names (p=.07) and on stopping dates (p=.0015). Even though women tended to overstate duration of OC use, recall was accurate enough to explore the presence of a moderately strong duration response relationship. This study showed that prescriber data should not be the only data source of a case control study and that they indeed complement women's histories.
