R/plot.IRT.informationCurves.R

In alexanderrobitzsch/TAM: Test Analysis Modules

## File Name: plot.IRT.informationCurves.R
## File Version: 9.08

#############################################################################
plot.IRT.informationCurves <- function(x, curve_type="test", ... )
{
    theta <- x$theta[,1]
    args <- list(...)
    xlim <- range(theta)
    #************************************
    # collect arguments for plot
    if ( sum( names(args)==c("xlim") )==1 ){
        xlim <- args$xlim
    }
    if ( sum( names(args)==c("xlim") )==0 ){
        xlim -> args$xlim
    }
    if ( sum( names(args)=="xlab")==0 ){
        args$xlab <- "theta"
    }
    if ( sum( names(args)=="ylab")==0 ){
        args$ylab <- "y"
    }


    #************************************************************
    #***** test information curve or se curve
    if ( curve_type %in% c("test", "se" ) ){

        if ( curve_type=="se" ){    y <- x$se_curve }
        if ( curve_type=="test" ){    y <- x$test_info_curve }

        y1 <- y[ ( theta > xlim[1] ) & ( theta < xlim[2] ) ]
        if ( is.null(args$ylim) ){
            ylim <- c( 0, max( y1, na.rm=TRUE ) )
            args$ylim <- ylim
                            }
        args$x <- theta
        args$y <- y
        args$type <- "l"
        do.call( graphics::plot, args )
    }
    #************************************************************
    #*********
    # add item information curves here ...

}
#############################################################################