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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.