need help in finding value of discrimination

Hello Sir/ma?am
I am snehali, doing IRT analysis for 2pl model.
1)I have data of 38 students with 40 questions.
2)I find value of theta(ability) of student
Formula = ln(total_count/(1-total_count))
At student level
3)difficulty?of questions (item difficulty)
Formula = ln(total_count/(1-total_count))
4)Find probability of Item difficulty by using following code
function (items)
{
????????????? ncases <- nrow(items)
????????????? item.mean <- colMeans(items, na.rm = TRUE)
????????????? item.mean[item.mean < (1/ncases)] <- 1/ncases
????????????? irt.item.diff.rasch <- log((1/item.mean) - 1)
}
5)Now need to find?item discrimination ,this is code from?package psych
and not understand value of x,diff,item.diff,theta,scores
?
?
function (item.diff, theta, items)
{
????????????? 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
}
Your reply is very important it will be great help for me


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