Drift {sasLM}

Drift defined by Lan and DeMets for Group Sequential Design

Description

Calculate the drift value with given upper bounds (z-valuse), times of test, and power.

Usage

  Drift(bi, ti=NULL, Power=0.9)

Arguments

bi

upper bound z-values

ti

times of test. These should be in the range of [0, 1]. If omitted, even-interval is assumed.

Power

target power at the final test

Details

It calculates the drift value with given upper bound z-values, times of test, and power. If the times of test is not given, even-interval is assumed. mvtnorm::pmvt (with noncentrality) is better than pmvnorm in calculating power and sample size. But, Lan-DeMets used multi-variate normal rather than multi-variate noncentral t distributionh. This function followed Lan-DeMets for the consistency with previous results.

Value

Drift value for the given condition

Author(s)

Kyun-Seop Bae [e-mail]

References

Reboussin DM, DeMets DL, Kim K, Lan KKG. Computations for group sequential boundaries using the Lan-DeMets function method. Controlled Clinical Trials. 2000;21:190-207.

Examples

  Drift(seqBound(ti=(1:5)/5)[, "up.bound"])