R/itemfit_sx2_calc_scoredistribution_R.R

In CDM: Cognitive Diagnosis Modeling

## File Name: itemfit_sx2_calc_scoredistribution_R.R
## File Version: 0.04


##########################################################################
# calculate distribution of sum score
itemfit_sx2_calc_scoredistribution_R <- function( pjk )
{
    # pjk .... [ TP, I, 2 ]   ... [ theta points, items, 2 categories ]
    P1 <- pjk[,,2]
    Q1 <- pjk[,,1]
    TP <- nrow(P1)
    I <- ncol(P1)
    score <- seq( 0, I, 1 )
    scoredistribution <- matrix(NA, TP, I+1 )
    scoredistribution[,1] <- Q1[,1]
    scoredistribution[,2] <- P1[,1]
    for (ii in 2:I){
        scoredistribution0 <- scoredistribution
        scoredistribution[,ii+1] <- P1[,ii] * scoredistribution0[,ii]
        for (kk in seq( 0, ii - 2, 1 ) ){
            scoredistribution[,ii-kk] <- Q1[,ii] * scoredistribution0[,ii-kk] +
                    P1[,ii] * scoredistribution0[,ii-kk-1]
        }
        scoredistribution[,1] <- Q1[,ii] * scoredistribution0[,1]
    }
    return(scoredistribution)
}
##############################################################################

.calc.scoredistribution.cdm <- itemfit_sx2_calc_scoredistribution_R