Survival Equivalence Program

Survival Equivalence Power/Sample Size

Function

Equivalence Survival is a program to calculate either estimates of sample size or power for equivalence studies. Exponential distributions are assumed and are specified using the ratio of the hazard for the treatment 1 to the hazard for treatment 2. The ratio of hazard rates describing equivalence is defined in the same way.

Program Code

The program is written in JavaScript.

Source

The program uses the following formula for the total sample size

N=(q(1-alpha)+q(Power))**2*Sum [1/(fi*ei)]/Delta**2

Where fi is the proportion of the sample in treatment i and ei are the event probabilities in treatment i, q is the inverse normal function and

Delta=log(HR(treat1/treat2)/HREquiv(treat1/treat2) )

Where HR(treat1/treat2) is the hazard ratio between treatment 1 and treatment 2 and HREquiv(treat1/treat2) is the hazard ratio defining equivalence.

Input Items

The user is prompted for values to the following items. For items that have initial default values set, the values are given in parentheses.

Significance level (.05)
One-sided test
Accrual time
Follow-up time
Competing Risk: the hazard of the competing risk random variable
Hazard rate in Treatment 1
Hazard ratios between treatment 1 and treatment 2. (HR(treat1/treat2).
Hazard ratios between treatment 1 and treatment 2 defining equivalence. (HREquiv(treat1/treat2).
Desired power for sample size estimation or total sample size for power estimation

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