R/likelihood_moments.R

In sirt: Supplementary Item Response Theory Models

## File Name: likelihood_moments.R
## File Version: 0.121

##****
likelihood_moments <- function( likelihood, theta=NULL )
{
    if ( is.null(theta) ){
        theta <- attr( likelihood, 'theta' )
    }
    nstud <- nrow(likelihood)
    TP <- ncol(likelihood)
    thetaM <- matrix( theta, nstud, TP, byrow=TRUE )
    likelihood <- likelihood / rowSums( likelihood )
    M1 <- rowSums( thetaM * likelihood )
    SD1 <- rowSums( thetaM^2 * likelihood )
    SD1 <- sqrt( SD1 - M1^2 )
    res <- list( M=M1, SD=SD1 )
    return(res)
}