This is for how to teach statistics and/or R. It is not for how to do analyses. There may be some IRT sources on the internet. You should search for them.
On Fri, Jun 28, 2019 at 1:47 AM hello <[email protected]> wrote: > 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 > > I’m protected online with Avast Free Antivirus. Get it here — it’s free > forever. > > > > > > > Sent from Mail for Windows 10 > > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > [[alternative HTML version deleted]] > > _______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-sig-teaching > [[alternative HTML version deleted]] _______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-sig-teaching
