factorial2x2 (version 0.2.0)

lgrkPower: Unstratified (ordinary) logrank power

Description

Computes the power for the unstratified (ordinary) logrank statistic for two group comparison.

Usage

lgrkPower(hr, nevent, alpha = 0.05, rprob = 0.5)

Arguments

hr

hazard ratio

nevent

expected number of events

alpha

two-sided significance level

rprob

randomization probability

Value

power

logrank power

Details

Uses the formula at the bottom of p.317 from Schoenfeld (Biometrika, 1981) where the beta should be 1 - beta. The formula is modified to assume that values of the hazard ratio less than 1 correspond to treatment efficacy. We do this because we only want to include the probability of rejecting the null in favor of efficacy, not inferiority as well.

References

Schoenfeld, D. The asymptotic properties of nonparametric tests for comparing survival distributions. Biometrika. 1981; 68: 316-319.

Examples

# NOT RUN {
 hr <- 0.5
 nevent <- 98
 lgrkPower(hr, nevent, alpha = 0.05,  rprob = 0.5)
 # $power
 # [1] 0.9293463

# }