convPN2P {lazy.irt}R Documentation

Convert Partial Credit Item Parameters in Nominal Format to Standard Format

Description

Convert Partial Credit Item Parameters in Nominal Format to Standard Format

Usage

convPN2P(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 Standard Format

Examples

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]