convP2PN {lazy.irt}R Documentation

Convert Partial Credit Item Parameters in Standard Format to Partial Credit Item Parameters in Nominal Format

Description

Convert Partial Credit Item Parameters in Standard Format to Partial Credit Item Parameters in Nominal Format

Usage

convP2PN(param, print = 0, DinP = 1, ctype = 0)

Arguments

param

Item Parameter Data Frame

print

= 1 to print result

DinP

= 1 to include D=1.7 in logistic function

ctype

= 1 to convert to type PN with c-parameters

Details

ICRF of category k of item j at theta, namely, p_{jk}(theta)
is defined as
p_{jk}(theta) = Ez_{jk}(theta) / sum_{k=0}^{ncat[j]-1} Ez_{jk}(theta)
where

if type = "PN" and ctype=0,
Ez_{jk}(theta) = exp( 1.7^DinP a_j k (theta - b_{jk}) )

, k=0,1, ..., ncat[j]-1
with b_{j0}=0.

if type = "PN" and ctype=1,
Ez_{jk}(theta) = exp( a_j k theta + c_{jk}) )

, k=0,1, ..., ncat[j]-1
with c_{j0}=0.

Note that if DinP=1, 1.7 will be used.

This b*_{jk} is the original step parameter and it is
the value of theta where P_{jk-1} and P_{jk} intersect.

Value

Partial Credit Item Parameter Data Frame in Nominal Format

Examples

temp <- irf( paramS1[4,], plot=1 )
temp <- irf( convP2PN(paramS1[4,]), plot=1 )

temp1 <- convP2PN(paramS1[4,])
temp2 <- convPN2P(temp1)
Print(paramS1[4,],temp1,temp2)

temp1 <- convP2PN(paramS1[4,], ctype=1)
temp2 <- convPN2P(temp1, ctype=1)
Print(paramS1[4,],temp1,temp2)



[Package lazy.irt version 0.1.3 Index]