R/IRT.truescore.R

In TAM: Test Analysis Modules

## File Name: IRT.truescore.R
## File Version: 9.07

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# IRT.truescore
IRT.truescore <- function( object, iIndex=NULL, theta=NULL, Q=NULL){
        irf <- IRT.irfprob(object)
        theta0 <- attr( irf, "theta" )[,1]
        dim_irf <- dim(irf)
        if ( is.null(iIndex) ){
            iIndex <- seq( 1, dim_irf[1] )
                        }
        irf <- irf[ iIndex,, ]
        K <- dim_irf[2] - 1
        irf[ is.na(irf)] <- 0
        I <- dim(irf)[1]

        if ( is.null(Q) ){
            Q <- matrix( seq(0,K), nrow=I, ncol=K+1, byrow=TRUE)
                }
        #*******
        # compute expected scores
        irf_K <- 0+0*irf
#        for (kk in 1:K){
#            irf_K[,kk+1,] <- kk
#                        }
        for (ii in 1:I){
            irf_K[ii,,] <- as.vector(Q[ii,])
                }


        TP <- dim_irf[3]
        I <- dim(irf)[1]
        vec <- rep(0,TP)

        for (ii in 1:I){
            # ii <- 1
            vec <- vec +  colSums( irf[ii,,] * irf_K[ii,,]  )
                        }
        dfr <- data.frame( "theta"=theta0, "truescore"=vec)
        #*******
        if ( ! is.null(theta) ){
            ind <- sum( ! ( theta >=min(theta0) ) & ( theta <=max(theta0) ) ) > 0
            if (ind){
                h1 <- "The true score cannot be computed for some theta values.\n"
                warning(paste0( h1, "  Use a larger theta grid in the fitted model.\n") )
                    }
            theta <- theta[ ( theta >=min(theta0) ) & ( theta <=max(theta0) ) ]
            TP1 <- length(theta)
            v1 <- 1
            v2 <- TP
            for (tt in 1:TP){
                v1 <- ifelse( theta > theta0[tt], tt, v1 )
                v2 <- ifelse( theta < theta0[TP-tt+1], TP-tt+1, v2 )
                            }
            vec <- dfr$truescore[ v1 ] +  ( dfr$truescore[ v2 ] - dfr$truescore[ v1 ] ) *
                        ( theta - dfr$theta[ v1 ] ) / ( dfr$theta[ v2 ] - dfr$theta[ v1 ] )
            dfr <- data.frame( "theta"=theta, "truescore"=vec)
                            }
        return(dfr)
            }
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