1\name{ciapower} 2\alias{ciapower} 3\title{ 4Power of Interaction Test for Exponential Survival 5} 6\description{ 7Uses the method of Peterson and George to compute the power of an 8interaction test in a 2 x 2 setup in which all 4 distributions are 9exponential. This will be the same as the power of the Cox model 10test if assumptions hold. The test is 2-tailed. 11The duration of accrual is specified 12(constant accrual is assumed), as is the minimum follow-up time. 13The maximum follow-up time is then \code{accrual + tmin}. Treatment 14allocation is assumed to be 1:1. 15} 16\usage{ 17ciapower(tref, n1, n2, m1c, m2c, r1, r2, accrual, tmin, 18 alpha=0.05, pr=TRUE) 19} 20\arguments{ 21\item{tref}{ 22time at which mortalities estimated 23} 24\item{n1}{ 25total sample size, stratum 1 26} 27\item{n2}{ 28total sample size, stratum 2 29} 30\item{m1c}{ 31tref-year mortality, stratum 1 control 32} 33\item{m2c}{ 34tref-year mortality, stratum 2 control 35} 36\item{r1}{ 37\% reduction in \code{m1c} by intervention, stratum 1 38} 39\item{r2}{ 40\% reduction in \code{m2c} by intervention, stratum 2 41} 42\item{accrual}{ 43duration of accrual period 44} 45\item{tmin}{ 46minimum follow-up time 47} 48\item{alpha}{ 49type I error probability 50} 51\item{pr}{ 52set to \code{FALSE} to suppress printing of details 53}} 54\value{ 55power 56} 57\section{Side Effects}{ 58prints 59} 60\section{AUTHOR}{ 61Frank Harrell 62 63 64Department of Biostatistics 65 66 67Vanderbilt University 68 69 70\email{f.harrell@vanderbilt.edu} 71} 72\references{ 73Peterson B, George SL: Controlled Clinical Trials 14:511--522; 1993. 74} 75\seealso{ 76\code{\link{cpower}}, \code{\link{spower}} 77} 78\examples{ 79# Find the power of a race x treatment test. 25\% of patients will 80# be non-white and the total sample size is 14000. 81# Accrual is for 1.5 years and minimum follow-up is 5y. 82# Reduction in 5-year mortality is 15\% for whites, 0\% or -5\% for 83# non-whites. 5-year mortality for control subjects if assumed to 84# be 0.18 for whites, 0.23 for non-whites. 85n <- 14000 86for(nonwhite.reduction in c(0,-5)) { 87 cat("\n\n\n\% Reduction in 5-year mortality for non-whites:", 88 nonwhite.reduction, "\n\n") 89 pow <- ciapower(5, .75*n, .25*n, .18, .23, 15, nonwhite.reduction, 90 1.5, 5) 91 cat("\n\nPower:",format(pow),"\n") 92} 93} 94\keyword{survival} 95\keyword{htest} 96\concept{power} 97\concept{study design} 98