"irt.discrim" <-
function(item.diff,theta,items) {
#find the item discrimination parameter (beta)
#find the item discrimination parameter -- optimized by item.discrim
irt.item.discrim <- function(x,diff,theta,scores) {
fit <- -1*(log(scores/(1+exp(x*(diff-theta))) + (1-scores)/(1+exp(x*(theta-diff)))))
mean(fit,na.rm=TRUE)
}
nitems <- length(item.diff)
discrim <- matrix(NaN,nitems,2)
for (i in 1:nitems) {
item.fit <- optimize(irt.item.discrim,c(-5,5),diff=item.diff[i],theta=theta,scores = items[,i])
discrim[i,1] <- item.fit$minimum
discrim[i,2] <- item.fit$objective}
irt.discrim <- discrim
}
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