Generalised Partial Credit Model Derived Probabilities

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Description

Calculate vector of probabilities of success from person and item parameters under the Generalised Partial Credit Model.

Usage

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  gpcm(theta=NULL,alpha=NULL,delta=NULL,n=NULL)

Arguments

theta

Theta parameter

alpha

Alpha parameter

delta

Vector of delta parameters

n

Number of item categories

Details

The delta parameters are the intersection points of adjacent category information functions. There should be one less delta parameter than categories. Assumes that the location parameter is zero

Value

Vector of probabilities of success

Examples

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## Generalized Partial Credit Model
## Item parameters from Embretson & Reise (2000, p. 112) item 5
theta <- 1
alpha <- .683
delta <- c(-3.513,-.041,.182)
n <- 4
gpcm(theta,alpha,delta,n)