Agreement of self-reported estrogen use with prescription data: an analysis of women from the Kuopio Osteoporosis Risk Factor and Prevention Study .
Self-reported data are usually used for the evaluation of the effects of hormone therapy in population studies. We examined the agreement between self-reported hormone therapy use and nationwide prescription data from the Social Insurance Institution of Finland to evaluate the accuracy of self-reports. The 10-year questionnaire of the population-based Kuopio Osteoporosis Study was sent in 1999 to 12,562 women aged 57 to 67 years; 11,377 women who completed questionnaires were eligible for analysis. We asked women whether they had been taking estrogen hormone therapy as a gel, plaster, or tablet for the treatment of climacteric symptoms or osteoporosis and if the answer was yes, to specify the brand and duration of treatment for each year from 1994 to 1999. Among the 11,377 women, 3,105 (27.3%) reported the use of an estrogen-based preparation in 1996 to 1999, and 97.6% were confirmed by Social Insurance Institution of Finland to have been prescribed hormone therapy during that time. In these women the median duration of use was 32 months (range, 1-41), according to Social Insurance Institution of Finland data. An additional 1,738 women had been prescribed hormone therapy for short periods, but those women did not report it. The duration of self-reported hormone therapy use was compared to the duration of prescriptions. A difference of 3 months or less per year was observed in 63.4% to 77.0% of women during the years 1996-1998. A postal inquiry is a reliable method of recording long-term hormone therapy use.