probgrm {lordif}

calculates item response probabilities according to GRM

Description

Calculates a matrix of item response probabilities over a grid of theta values for an item

Usage

probgrm(theta, a, cb)

Arguments

theta

a vector of theta values (e.g., quadrature points)

a

a slope parameter value

cb

a vector of category threshold values

Details

The Graded Response Model (Samejima, 1969) is assumed.

Value

Returns a matrix of item response probabilities. The first dimension corresponds to the length of theta.

Author(s)

Seung W. Choi <[e-mail]>

References

Samejima, F. (1969). Estimation of latent ability using a response pattern of graded scores. Psychometrika Monograph, 17.

See Also

calcprob, probgpcm

Examples

  probgrm(seq(-4,4,.1), 1.5, c(-1.2,0.5,1.5))