[R] about IRT simulation

[Dimitris Rizopoulos]

have a look at function rmvlogis() from package ltm, e.g.,

library(ltm)

p <- 5
n <- 10
a <- rnorm(p, 0.8, 0.04)
b <- rnorm(p, 0, 1)

?rmvlogis
rmvlogis(n, cbind(b, a))


I hope it helps.

Best,
Dimitris


On 3/11/2010 5:03 AM, Helena wrote:
> hello R:
> we have a two-parameter IRT simulation code. The goal is to generate a
> response matrix.But the "for" part doesn't run. we don't know what is wrong
> with it.
>
> Thanks so much~~~
>
> I<- 10
> J<- 5
> response<- matrix(0, 10, 5)
> pij<- function(a,b,theta)
> {
> a<- rnorm(J, 0.8, 0.04)
> a
> b<- rnorm(J, 0, 1)
> b
> theta<- rnorm(I, 0,1)
> theta
> for( i in 1:I ) {
> 	for( j in 1:J ) {
> ptemp<- runif(1)
> 		pij<- exp(a[j]*(theta[i]-b[j]))/(1+exp(a[j]*(theta[i]-b[j])))
> 	response[i,j]<-ifelse(pij(b=b[j], a=a[j], theta[i])<  ptemp , 0 ,1)
>
> }
> }
> }
> response	
>
>
>
> helena
>
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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