>>>>> hello >>>>> on Fri, 28 Jun 2019 11:16:50 +0530 writes:
Dear Snehali, this is the wrong mailing list (this list is for TEACHERS / Instructors of Statistics and R, using R in class). Please use the R-help mailing list instead, and see also https://www.r-project.org/help.html Best regards, Martin Maechler > 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]] > _______________________________________________ > R-sig-teaching@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-sig-teaching _______________________________________________ R-sig-teaching@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-sig-teaching
