## File: ciapower.Rd

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hmisc 4.2-0-1
 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394959697 \name{ciapower} \alias{ciapower} \title{ Power of Interaction Test for Exponential Survival } \description{ Uses the method of Peterson and George to compute the power of an interaction test in a 2 x 2 setup in which all 4 distributions are exponential. This will be the same as the power of the Cox model test if assumptions hold. The test is 2-tailed. The duration of accrual is specified (constant accrual is assumed), as is the minimum follow-up time. The maximum follow-up time is then \code{accrual + tmin}. Treatment allocation is assumed to be 1:1. } \usage{ ciapower(tref, n1, n2, m1c, m2c, r1, r2, accrual, tmin, alpha=0.05, pr=TRUE) } \arguments{ \item{tref}{ time at which mortalities estimated } \item{n1}{ total sample size, stratum 1 } \item{n2}{ total sample size, stratum 2 } \item{m1c}{ tref-year mortality, stratum 1 control } \item{m2c}{ tref-year mortality, stratum 2 control } \item{r1}{ \% reduction in \code{m1c} by intervention, stratum 1 } \item{r2}{ \% reduction in \code{m2c} by intervention, stratum 2 } \item{accrual}{ duration of accrual period } \item{tmin}{ minimum follow-up time } \item{alpha}{ type I error probability } \item{pr}{ set to \code{FALSE} to suppress printing of details }} \value{ power } \section{Side Effects}{ prints } \section{AUTHOR}{ Frank Harrell Department of Biostatistics Vanderbilt University \email{f.harrell@vanderbilt.edu} } \references{ Peterson B, George SL: Controlled Clinical Trials 14:511--522; 1993. } \seealso{ \code{\link{cpower}}, \code{\link{spower}} } \examples{ # Find the power of a race x treatment test. 25\% of patients will # be non-white and the total sample size is 14000. # Accrual is for 1.5 years and minimum follow-up is 5y. # Reduction in 5-year mortality is 15\% for whites, 0\% or -5\% for # non-whites. 5-year mortality for control subjects if assumed to # be 0.18 for whites, 0.23 for non-whites. n <- 14000 for(nonwhite.reduction in c(0,-5)) { cat("\n\n\n\% Reduction in 5-year mortality for non-whites:", nonwhite.reduction, "\n\n") pow <- ciapower(5, .75*n, .25*n, .18, .23, 15, nonwhite.reduction, 1.5, 5) cat("\n\nPower:",format(pow),"\n") } } \keyword{survival} \keyword{htest} \concept{power} \concept{study design}