# Extract Item Parameters `itm` is a generic function which extracts a data frame containing the item parameters of two forms being equated in the original scale and item parameters of the first form converted in the scale of the second form. ```r itm(x, ...) ## S3 method for class 'eqc' itm(x, ...) ## S3 method for class 'eqclist' itm(x, link, ...) ## S3 method for class 'ceqc' itm(x, ...) ## S3 method for class 'ceqclist' itm(x, path, ...) ## S3 method for class 'meqc' itm(x, link, bistype = NULL, ...) ``` ## Arguments - `x`: object of the class `eqc` returned by function `direc` or of the class `eqclist` returned by function `alldirec` or of the class `ceqc` and `ceqclist` returned by function `chainec` or of the class `meqc` return by function `bisectorec`. - `link`: a character string with the names of the two forms being linked separated by a dot (e.g. "`test1.test3`"). - `path`: a character string with the names of the forms that constitute the path separated by a dot (e.g. "`test1.test2.test3`"). - `bistype`: bisector type. It should be `weighted` or `unweighted`. It could be `NULL` if only one type was computed by function `bisectorec`. - ``...``: further arguments passed to or from other methods. ## Returns A data frame containing item names (`Item`), item parameters of the first form (e.g. `test1`), item parameters of the last form (e.g. `test3`), and item parameters of the first form converted in the scale of the last form (e.g. `test1.as.test3`). ## Author(s) Michela Battauz ## See Also `convert`, `alldirec`, `bisectorec`, `chainec`, `direc`, `modIRT` ## Examples ```r # the following code uses item parameter estimates previously obtained # for examples that start from item response data see function modIRT # two-parameter logistic model data(est2pl) test<-paste("test", 1:5, sep = "") mod2pl <- modIRT(coef = est2pl$coef, var = est2pl$var, names = test, display = FALSE) # direct equating coefficients between forms 1 and 2 using the Haebara method l12 <- direc(mods = mod2pl, which = c(1,2), method = "Haebara") # all direct equating coefficients using the Haebara method direclist2pl <- alldirec(mods = mod2pl, method = "Haebara") # compute all chain equating coefficients of length 3 chainec3 <- chainec(r = 3, direclist = direclist2pl) # compute chain equating coefficients for path 1,2,3,4 pth1 <- paste("test", 1:4, sep = "") chainec1 <- chainec(direclist = direclist2pl, pths = pth1) # compute chain equating coefficients for path 1,5,4 pth2 <- c(paste("test", c(1,5,4), sep = "")) chainec2 <- chainec(direclist = direclist2pl, pths = pth2) # create a list of objects of class ceqc ecall <- c(chainec1, chainec2) # compute bisector and weighted bisector coefficients allec <- bisectorec(ecall = ecall, weighted = TRUE, unweighted = TRUE) # extract item parameters itm(l12) itm(direclist2pl, link = "test1.test2") itm(chainec3, path = "test1.test2.test3") itm(allec, bistype = "weighted") ```

itm function