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To the Editor: Dr D’Amico et al¹ report a statistically significant improvement in survival with the addition of 6 months of androgen suppression therapy to 70-Gy radiation therapy for patients with clinically localized prostate cancer. However, they note a P value of.04 for the log-rank test of overall survival, while the 95% confidence intervals for 5-year survival in the treatment groups overlap widely (80%-95% with androgen suppression and 68%-88% without it). The reason for this discrepancy is not clear. I wonder if the authors are actually reporting a 1-sided P value (2-sided P values are specified in the "Methods" section only for their power calculations), or if the difference reflects the log-rank test’s exaggeration of changes in the tail of the survival curve, where statistical variability is greater due to fewer patients at risk.² The latter possibility would be suggested if the generalized Wilcoxon test is not statistically significant, since . . . [Full Text of this Article]

Carl D. Atkins, MD
c3atkins@optonline.net
Rockville Centre, NY

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