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Table 1 Impact of long term survival and delayed clinical effect on statistical power and study duration

From: Statistical issues and challenges in immuno-oncology

  PHM PHCRM NPHM NPHCRM
Cure rate 0.10 vs. 0.18 0.10 vs. 0.17
Delayed clinical effect (month) 3 3
Sample size 680 680 680 680
Number of events 512 512 512 512
Hazard ratio (pre- and post- separation) 0.75 0.75 1/0.75 1/0.75
Type I error 0.05 0.05 0.05 0.05
Power 0.90 0.90 0.70 0.70
Accrual duration (month) 34 34 34 34
Study duration (month) 48 55 47 54
  1. A study designed to detect a hazard ratio of 0.75 with two-sided type I error rate of 5% and power of 90% requires 512 events under exponential assumption. The study would take 48 months with accrual rate of 20 patients per month for 34 months. When a cured fraction of patients exists in both arms, the study duration is extended to 55 months. A delayed separation in overall survival effect would lead to a loss in power. The presence of both long term survival and delayed clinical effect would lead to an underpowered and lengthy study.