## File Name: stratified_cronbach_alpha_compute_alpha.R
## File Version: 0.06
#** compute alpha
stratified_cronbach_alpha_compute_alpha <- function( data )
{
# covariance
c1 <- stats::cov( data, use="pairwise.complete.obs" )
# mean covariance
c1a <- c1
diag(c1a) <- 0
I <- ncol(data)
mc <- sum(c1a) / ( I^2 - I )
# mean and variance
mv <- mean( diag(c1) )
alpha <- I*mc / ( mv + (I-1)*mc )
mean.tot <- mean( rowSums(data), na.rm=TRUE )
var.tot <- stats::var( rowSums(data), na.rm=TRUE )
res <- list( I=I, alpha=alpha, mean.tot=mean.tot, var.tot=var.tot )
return(res)
}
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