plotCRM {EstCRM} R Documentation

## Draw Three-Dimensional Item Category Response Curves

### Description

This function draws the 3D item category response curves given the item parameter matrix and the maximum and minimum possible values that examinees can get as a score for the item. This 3D representation is an extension of 2D item category response curves in binary and polytomous IRT models. Due to the fact that there are many possible response categories, another dimension is drawn for the response categories in the 3D representation.

### Usage

plotCRM(ipar, item, min.item, max.item)


### Arguments

 ipar a matrix with m rows and three columns, with m denoting the number of items. The first column is the a parameters, the second column is the b parameters, and the third column is the alpha parameters item item number, an integer between 1 and m with m denoting the number of items min.item a vector of length m indicating the minimum possible score for each item. max.item a vector of length m indicating the maximum possible score for each item.

### Value

 irf a 3D theoretical item category response curves

### Author(s)

Cengiz Zopluoglu

EstCRMitem for estimating item parameters, EstCRMperson for estimating person parameters, fitCRM for computing item-fit residual statistics and drawing empirical 3D item category response curves, simCRM for generating data under CRM.

### Examples



data(EPIA)

##Define the vectors "max.item" and "min.item". The maximum possible
##score was 112 and the minimum possible score was 0 for all items

min.item <- c(0,0,0,0,0)
max.item <- c(112,112,112,112,112)

##Estimate item parameters

CRM <- EstCRMitem(EPIA, max.item, min.item, max.EMCycle = 500, converge = 0.01)
par <- CRM\$param

##Draw theoretical item category response curves for Item 2
plotCRM(par,2,min.item, max.item)



[Package EstCRM version 1.4 Index]