The validity of self-reported use of. hormone replacement therapy among Danish nurses

Background. Recent findings from randomized clinical trials on the effects of hormone replacement therapy (HRT) among postmenopausal women contradict findings from observational studies indicating a protective.-effect on the development of cardiovascular disease. Most observational studies on HRT are based on self-reported data, although data on the validity of HRT in postmenopausal women are sparse. Methods. We examined self-reported HRT use from questionnaires administered in 1993 (n = 2694) and again in 1999 (n = 2666) to a cohort of Danish nurses living in two Danish counties compared with prescription-reimbursement data from two administrative databases through the Danish National Health Service. Results. The sensitivity and specificity of the self-reported, current HRT use in 1993 were 78.4% [95% confidence interval (95%CI) 75.4-81.4] and 98.4% (95% CI 97.8-98.9), respectively. In 1999, the estimates were 74.8% (95% CI 72.0-77.7) and 98.0% (95% CI 97.3-98.8), respectively. None of the factors examined-including age, alcohol intake, physical activity, smoking, presence of hypertension, and body mass index-was strongly associated with validity. We found a relatively high validity of self-reported data on HRT use. Furthermore, agreement between self-reported and registry-based data was not strongly associated with a range of demographic and lifestyle factors. Conclusion. These findings suggest that use of self-reported data is not an important contributor to the apparent discrepancy between observational studies and randomized trials on the. cardiovascular effects of HRT use.