extract.deltas {WrightMap}

Extract Master's Delta parameters from a TAM model.

Description

This function takes as its input a TAM object. It adds reads the TAM item parameters and organizes them into a matrix that can be used as input in the CCCfit function.

Usage

extract.deltas(tamObject)

Arguments

tamObject

TAM object containing the results of a a Rasch model or Partial Credit model.

Details

This function organizes the item parameter results into a matrix where each row is contains the parameters associated with an item and each columns is contains the parameters associated with a specific step (score 0 vs score 1, score 1 vs score 2, etc.). The resulting matrix will have as many rows as items and as many columns as the maximum number of steps among the items.

Value

A matrix in which each row is an item and each column is a step

Author(s)

David Torres Irribarra

References

Masters, G. N. (1982). A Rasch model for partial credit scoring. Psychometrika, 47(2), 149-174.

See Also

CCCfit make.thresholds

Examples

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.

## The function is currently defined as
function (tamObject) 
{
    delta.long <- tamObject$xsi
    n.deltas <- apply(tamObject$B, 1, max)
    delta.mat <- matrix(NA, nrow = length(n.deltas), ncol = max(n.deltas))
    matCoords.row <- rep(1:length(n.deltas), n.deltas)
    matCoords.col <- c()
    for (i in 1:length(n.deltas)) {
        for (j in 1:n.deltas[i]) {
            matCoords.col <- c(matCoords.col, j)
        }
    }
    delta.long$matCoords.row <- matCoords.row
    delta.long$matCoords.col <- matCoords.col
    for (k in 1:nrow(delta.long)) {
        delta.mat[delta.long$matCoords.row[k], delta.long$matCoords.col[k]] <- delta.long$xsi[k]
    }
    delta.mat
  }