Kim-DeMets (power) Spending Function

The function sfPower() implements a Kim-DeMets (power) spending function. This is a flexible, one-parameter spending function recommended by Jennison and Turnbull (2000).

A Kim-DeMets spending function takes the form $$f(t;\alpha,\rho)=\alpha t^\rho$$ where $\rho$ is the value passed in param. See examples below for a range of values of $\rho$ that may be of interest (param=0.75 to 3 are documented there).

Usage

sfPower(alpha, t, param)

Arguments

alpha: Real value $> 0$ and no more than 1. Normally, alpha=0.025 for one-sided Type I error specification or alpha=0.1 for Type II error specification. However, this could be set to 1 if for descriptive purposes you wish to see the proportion of spending as a function of the proportion of sample size/information.
t: A vector of points with increasing values from 0 to 1, inclusive. Values of the proportion of sample size/information for which the spending function will be computed.
param: A single, positive value specifying the $\rho$ parameter for which Kim-DeMets spending is to be computed; allowable range is (0,50]

Value

An object of type spendfn. See vignette("SpendingFunctionOverview") for further details.

Note

The gsDesign technical manual is available at https://keaven.github.io/gsd-tech-manual/.

References

Jennison C and Turnbull BW (2000), Group Sequential Methods with Applications to Clinical Trials. Boca Raton: Chapman and Hall.

Author

Keaven Anderson keaven_anderson@merck.com