R/regintR2.R

In chrisaberson/pwr2ppl: Power Analyses for Common Designs (Power to the People)

#'Compute Power for Regression Interaction (R2 Change Approach)
#'@param R2Mod Full Model R2
#'@param R2Ch Change in R2 Added by Interaction
#'@param mod_pred Full Model Number of Predictors
#'@param ch_pred Change Model Number of Predictors
#'@param nlow starting sample size
#'@param nhigh ending sample size
#'@param by incremental increase in sample (e.g. nlow = 10, nhigh = 24, by = 2, produces estimates of 10, 12, and 14)
#'@param alpha Type I error (default is .05)
#'@examples
#'regintR2(R2Mod=.092,R2Ch=.032,mod_pred=3, ch_pred=1,nlow=100,nhigh=400,by=20)
#'@return Power for Regression Interaction (R2 Change Approach)
#'@export
#'
#'


regintR2<-function(R2Mod, R2Ch, mod_pred, ch_pred,nlow, nhigh, by =1, alpha=.05)
{
result <- data.frame(matrix(ncol = 3))
colnames(result) <- c("n","R2 Change)","Power")
for(n in seq(nlow,nhigh, by)){
df_denom <- (n - mod_pred)-1
f2 <- R2Ch/(1-R2Mod)
lambda = f2*df_denom
minusalpha<-1-alpha
Ft<-stats::qf(minusalpha, ch_pred, df_denom)
Power<-round(1-stats::pf(Ft, ch_pred, df_denom,lambda),4)
result[n, 1]<-n
result[n, 2]<-R2Ch
result[n, 3]<-Power}
output<-na.omit(result)
rownames(output)<- c()
output}