exitprob {lrstat}

Stagewise exit probabilities

Description

Obtains the stagewise exit probabilities for both efficacy and futility stopping.

Usage

exitprob(b, a = NA, theta = 0, I = NA)

Arguments

b

Upper boundaries on the z-test statistic scale.

a

Lower boundaries on the z-test statistic scale. Defaults to c(rep(-6.0, kMax-1), b[kMax]) if left unspecified, where kMax = length(b).

theta

Stagewise parameter of interest, e.g., -U/V for weighted log-rank test, where U is the mean and V is the variance of the weighted log-rank test score statistic at each stage. For proportional hazards and conventional log-rank test, use the scalar input, theta = -log(HR). Defaults to 0 corresponding to the null hypothesis.

I

Stagewise cumulative information, e.g., V, the variance of the weighted log-rank test score statistic at each stage. For conventional log-rank test, information can be approximated by phi*(1-phi)*D, where phi is the probability of being allocated to the active arm, and D is the total number of events at each stage. Defaults to seq(1, kMax) if left unspecified.

Value

A list of stagewise exit probabilities:

• exitProbUpper: The vector of efficacy stopping probabilities

• exitProbLower: The vector of futility stopping probabilities.

Author(s)

Kaifeng Lu, [e-mail]

Examples

exitprob(b = c(3.471, 2.454, 2.004), theta = -log(0.6),
         I = c(50, 100, 150)/4)

exitprob(b = c(2.963, 2.359, 2.014),
         a = c(-0.264, 0.599, 2.014),
         theta = c(0.141, 0.204, 0.289),
         I = c(81, 121, 160))