IRF: Plot item response curves
In seonghobae/flirt.x32: Flexible Item Response Theory Modeling

Description Usage Arguments Details Author(s) See Also Examples

A function to plot item response curves as a function of latent ability for unidimensional 1PL, 2PL, and 3PL models.

1 2	## S3 method for class 'flirt' IRF(alpha=NULL, beta, guess=NULL , inside=NULL, ylim=NULL)

`alpha`	α_i parameter estimates. If `NULL`, α_i=1
`beta`	β_i parameter estimates
`guess`	c_i (guessing) parameter estimates. If `NULL`, c_i=0
`inside`	If `TRUE`, P_i = c_i + \frac{(1-c_i)}{1+ exp(-α_i (θ_p + β_i))} is estimated
`ylim`	the y limits of the plot.

For single and multiple items.

Minjeong Jeon <jeon.117@osu.edu>

flirt

library(flirt)

## verbal aggression data

data(verb2)

# 2-dimensional 2PL model  for binary data:  a(th+b) parameterization
result2 <- flirt(data=verb2, loading=list(on=T, inside=T), control=list(nq=5) )
alpha <- result2@pars[1:24,2]
beta <- result2@pars[25:48,1]

# item resonse curve for four items              
IRF(beta=beta[1:4], alpha=alpha[1:4], inside=T)