R/tam_mml_inits_xsi.R

In TAM: Test Analysis Modules

## File Name: tam_mml_inits_xsi.R
## File Version: 0.11

tam_mml_inits_xsi <- function(A, resp.ind, ItemScore, xsi.inits, xsi.fixed,
        est.xsi.index, pweights, xsi.start0, xsi, resp, addnumb=.5 )
{
    # starting values for xsi
    maxAi <-  - apply(-(A), 3, tam_rowMaxs, na.rm=TRUE)
    personMaxA <- resp.ind %*% maxAi
    ItemMax <- crossprod( personMaxA, pweights )

    #-- needed for 2PL estimation maximum score in resp, equal categories?
    maxscore.resp <- apply( resp, 2, max )
    if ( ncol(resp)>1){
        sd.maxscore.resp <- stats::sd(maxscore.resp)
    } else {
        sd.maxscore.resp <- 0
    }
    equal.categ <- if( sd.maxscore.resp > 1E-6 ){ FALSE } else { TRUE  }

    #--- inits for xsi
    xsi[est.xsi.index] <- - log(abs(( ItemScore[est.xsi.index]+addnumb)/
                    (ItemMax[est.xsi.index]-ItemScore[est.xsi.index]+addnumb) ) )
    # starting values of zero
    if( xsi.start0 ){
        xsi <- 0*xsi
    }

    #log of odds ratio of raw scores
    if ( ! is.null(xsi.inits) ){
        xsi[ xsi.inits[,1] ] <- xsi.inits[,2]
    }
    if ( ! is.null( xsi.fixed ) ){
        xsi[ xsi.fixed[,1] ] <- xsi.fixed[,2]
    }

    #--- OUTPUT
    res <- list(xsi=xsi, personMaxA=personMaxA, ItemMax=ItemMax, equal.categ=equal.categ)
    return(res)
}