Discussion on "Statistical Issues Arising in the Women's Health Initiative".
Biometrics. 2005;61(4):922-30.
ABSTRACT
We thank Xihong Lin for the opportunity to discuss Ross Prentice and collaborators' interesting paper. The Women's Health Initiative (WHI) randomized hormone trials evaluated the effect of postmenopausal hormone therapy on the risk of various diseases (WHI Study Group, 1998). In the first WHI trial, women were randomly assigned to either estrogen plus progestin or placebo. The rate of coronary heart disease (CHD) in the hormone group was 1.24 times ($95% CI: 0.97, 1.60) that in the placebo group (Manson et al., 2003).
This result was surprising because large observational studies previously suggested a reduced risk of CHD among hormone users. Among the largest of these studies were the Nurses' Health Study (NHS) in the United States (Stampfer et al., 1991; Grodstein et al., 1996, 2000; Grodstein, Manson, and Stampfer, 2001) and a study based on the General Practice Research Database (GPRD) in the United Kingdom (Varas-Lorenzo et al., 2000).
We investigate possible sources of the discrepancy by reanalyzing the observational study data using an approach that mimics as closely as possible the published analyses of the WHI randomized trial. We then compare our approach with Prentice and collaborators'. Originally we had planned to provide reanalyses of both the NHS and GPRD data. Unfortunately, our reanalysis of the NHS data is not yet complete, so we report only the GPRD results.