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
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
