To the Editor: In their cohort study, Dr Schroth and colleagues1 reported an association between CYP2D6 polymorphisms and breast cancer outcomes among women treated with tamoxifen. Although the authors described their study as adequately powered, it appears that their power calculations did not account for the substantial overlap between the outcomes reported in this study and the outcomes described in 2 earlier reports.2,3 This overlapping sample violates the independent trials assumption that underlies all frequentist statistics, including power calculations.
Lash TL. Association Between CYP2D6 Polymorphisms and Breast Cancer Outcomes. JAMA. 2010;303(6):516-517. doi:10.1001/jama.2010.92