powexp2: Power for two sample exponential (or logrank)

In raredd/desmon: Functions for design and monitoring of clinical trials

Power for two sample exponential (or logrank)

Description

Computes power for a stratified test comparing two groups with exponential failure time distributions. The power can also be used for the logrank test under proportional hazards.

Usage

powexp2(
  acc.rate,
  acc.per,
  add.fu,
  l1,
  r1o2,
  p1,
  prop.strat = rep(1, length(l1)),
  alpha2 = 0.05,
  nullh = 1
)

Arguments

acc.rate	Accrual rate
acc.per	Accrual period
add.fu	Additional follow-up after the end of accrual before data are analyzed
l1	Hazard rates in group 1 (one per stratum)
r1o2	Hazard ratios for group 1 over group 2; either length 1 or length = number of strata
p1	Proportion in group 1; either length 1 or length = number of strata. Can be different for different strata.
prop.strat	Proportion of the total sample in each stratum
alpha2	Two-sided type I error rate
nullh	Null hypothesis hazard ratio (1 over 2)

Details

Computes the power for a stratified test in the two sample exponential problem. The test is actually based on the optimally weighted average of the log hazard ratio estimates from each stratum. Unlike other sample size functions, any of the input parameters (except alpha2) can take different values for different strata. For example, the proportion in each stratum can be specified through either prop.strat or by giving difference accrual rates for each stratum, and the follow-up time can be different for different stratum to allow for different strata to have opened or closed at different times.

Value

A vector of length 4 giving the overall expected standard error of with weighted average log hazard ratio (se), the expected value under the alternative of the weighted average log hazard ratio (me), the expected total number of failure events under the alternative (n.fail), and the power (power).

See Also

seqopr; powlgrnk; correl.power

Examples

powexp2(200, 2, 3, log(2) / 4, 1.5, 0.5)
powexp2(200, 2, 3, log(2) / 4, 1.33, 0.5)
powexp2(200, 2, 3, log(2) / 4, c(1.5, 1), 0.5, c(0.7, 0.3))
powexp2(10, 31.5, 13.75, c(log(2) / 6, log(2) / 8), c(1.4, 1.2), 0.5, c(0.9, 0.1))
powexp2(c(9, 1), 31.5, 13.75, c(log(2) / 6, log(2) / 8), c(1.4, 1.2), 0.5)

raredd/desmon documentation built on May 7, 2024, 3:46 p.m.