Table 3.

Theoretical Scenarios to Illustrate How Variations in Survival of the Control Cohort Impact on the Sample Size Required to Maintain Statistical Power

Scenario	A/E Ratio	Expected Outcome of Control Arm	Size Effect Studied	Absolute Benefit in Survival to Demonstrate the Same Benefit	Expected Outcome of Experimental Arm	Sample Size Required
Initial trial design	Not applicable	24 mo	1.25	6 mo	30 mo	455 patients per arm
No. of patients to demonstrate same maintenance of absolute benefit	1.5	36 mo	1.166	6 mo	40 mo	1685 patients per arm
No. of patients to demonstrate maintenance of effect size	1.5	36 mo	1.25	9 mo	45 mo	495 patients per arm

Abbreviation: A/E ratio, actual‐over‐expected ratio.

Calculations were made assuming an accrual rate of 20 patients per month and a follow‐up time of 24 months for the first scenario and 36 months for the latter 2 scenarios.