R/rrum.param.R

In CDM: Cognitive Diagnosis Modeling

## File Name: rrum.param.R
## File Version: 0.26



#***************************************************************
# RRUM parametrization
.rrum.param <- function( delta.summary, q.matrix )
{
    #---
    #  RRUM parametrization
    #  log( P(X=1) )=b0 + b1*alpha1 + b2 * alpha2
    #  RRUM:
    #  P(X=1)=pi * r1^( 1- alpha1) * r2^(1-alpha2)
    #=> log( P(X=1) )=log[ pi * r1 * r2 * r1^(-alpha1) * r2^(-alpha2) ]
    #=log( pi ) + log(r1) + log(r2) + -log(r1)*alpha1 + -log(r2) * alpha2
    #=> b1=-log(r1) and r1=exp( -b1 )
    #=> log(pi)=b0 + b1 + b2 and pi=exp( b0 + b1 + b2 )
    I <- nrow(q.matrix)
    K <- ncol(q.matrix)
    rrum.params <- matrix( NA, I, K+1 )
    rownames(rrum.params) <- delta.summary[ delta.summary$partype==0, "item" ]
    colnames(rrum.params) <- c( "pi", paste( "r_", colnames(q.matrix), sep="") )
    for (ii in 1:I){
        d.ii <- delta.summary[ delta.summary$itemno==ii, ]
        rrum.params[ii,"pi"] <- exp( sum( d.ii$est ) )
        rrum.params[ ii, which( q.matrix[ii,]==1) +1 ] <- exp( - d.ii$est[-1] )
    }
    return( rrum.params )
}