R/IRT.drawPV.R

In TAM: Test Analysis Modules

## File Name: IRT.drawPV.R
## File Version: 9.10


###################################################
# draw plausible values
IRT.drawPV <- function( object, NPV=5 )
{
    post1 <- IRT.posterior( object )
    theta <- attr( post1, "theta" )
    hwt <- as.matrix(post1)
    rownames(hwt) <- NULL
    attr(hwt,"theta") <- NULL
    attr(hwt,"prob.theta") <- NULL
    N <- nrow(hwt)
    TP <- nrow(theta)
    D <- ncol(theta)
    pvmatr <- matrix( NA, nrow=N, ncol=NPV*D )
    l1 <- NULL
    for (pp in 1:NPV){
        l1  <- c( l1, paste0("PV", pp, ".Dim",1:D) )
    }
    colnames(pvmatr) <- l1

    #********************************************
    # draw plausible values for uni-dimensional models
    if (D==1){
        theta <- matrix( theta, nrow=N, ncol=TP, byrow=TRUE )
        m1 <- rowSums( hwt * theta )
        sd1 <- sqrt( rowSums( hwt * theta^2 ) - m1^2 )
        for (pp in 1:NPV){
            pvmatr[,pp] <- stats::rnorm( N, mean=m1, sd=sd1 )
        }
    }
    #*************************************************
    # draw plausible values for multidimensional models
    if (D>1){
        Sigma <- matrix( 0, nrow=D, ncol=D)
        mu <- rep(0,D)
        for (nn in 1:N){
            # nn <- 1
            hwt.nn <- hwt[nn, ]
            for (dd in 1:D){
                mu[dd] <- sum( hwt.nn * theta[,dd] )
            }
            for (dd1 in 1:D){
                for (dd2 in dd1:D){
                    Sigma[dd1,dd2] <- sum( hwt.nn * theta[,dd1] * theta[,dd2] )
                    Sigma[dd1,dd2] <- Sigma[dd1,dd2] - mu[dd1]*mu[dd2]
                    Sigma[dd2,dd1] <- Sigma[dd1,dd2]
                }
            }
            pv_nn <- CDM::CDM_rmvnorm( NPV, mean=mu, sigma=Sigma )
            pvmatr[nn, ] <- as.vector( matrix( t(pv_nn), nrow=NPV*D, ncol=1,byrow=TRUE ))
        }
    }
    #-- end plausible value imputation function
    return(pvmatr)
}