similar to: Multilevel IRT Modelling

Dear all, I have the following problem: I have been using the routine "optim" in order to maximize a joint likelihood (basically a mixture with modeled weights) with quantitative variables..so far so good. Now I need to plug into the model a categorical variable (namely, age classes). Obviously, given the way optim works, it won't allow me to treat it "directly" (i.e.

Dear useRs, does any of you have suggestions on how to conduct a proper DIF analysis starting from a model of class gpcm (from the wonderful package ltm by prof. Rizopoulos)? difR will handle only dichotomous items, and I have a mix of dicho- and polytomous ones (that's why I chose the partial credit model). I also found the package lordif, but I'm not really sure if that's what I

hello R, This is about simulation in psychomtrics in IRT in R. I want to simulate b parameters(item difficulty) with moments of fixed values of mean, st.d, skewness and kurtosis. Is there any specific IRT package in R with those functions to control those moments? I have seen other programs that can control mean and st.d but not skewness and kurtosis. Thank you, helen L [[alternative HTML

Dear R-List, I tried to fit a partial credit model using the "pcmdat" from eRm-package comparing the results of mirt, eRm, ltm and winsteps. The results where quite different, though. I cannot figure out what went wrong and I do not know which result I can rely on. This is what I did in R library(mirt) #load(file="u3.RData")

I'm building R-3.1.1 (64 bit) from source on AIX 7.1. It was going well until I hit this: xlc_r -q64 -Wl,-brtl -Wl,-G -Wl,-bexpall -Wl,-bnoentry -lc -L/opt/freeware/lib64 -L/opt/freeware/lib -Wl,-blibpath:/opt/freeware/lib64:/opt/freeware/lib:/usr/lib:/lib -Wl,-bmaxdata:0x80000000 -o tools.so text.o init.o Rmd5.o md5.o signals.o install.o getfmts.o http.o gramLatex.o gramRd.o -lm make[6]:

Dear list, we are a statistical/epidemiological departement that - after a few years of rapid growth - finally is getting around to formulate a general data storage and retention policy - mainly to ensure that we can reproduce results from published papers/theses easier in the future, but also with the hope that we get more synergy between related projects. We have formulated what we

Hello, this is just a point of curiosity with me. I want a sequence of numbers from 64 to 70, omitting the 2nd and 4th numbers. I can do it these ways: > seq(64, 70)[-c(2, 4)] [1] 64 66 68 69 70 > foo <- 64:70 > foo[-c(2, 4)] [1] 64 66 68 69 70 But how come this doesn't work? > 64:70[-c(2, 4)] [1] 64 65 66 67 68 69 70 Just wondering. -- Stuart Luppescu -=- slu .at.

Hello all, I need to extract rows and columns from a data frame and put them in a matrix. In some cases, there are no rows in the data frame meeting the selection criteria. For those rows I want to put a row of 0's in the matrix. Here's my clumsy code: tab1.m1 <- matrix(0, nrow=2, ncol=4) tab1.m1[1,] <- ifelse(length(as.matrix(tab1[tab1$comp==the.comp & tab1$schlid==the.schl

Hello, This one is very perplexing. I have teacher observation data, with factors teacher ID, observer ID, component, grade and subject. When I do this, aov(data=ratings.prin.22, rating ~ obsid.f + tid.f + subject.f + grade.f + comp.f) I get this: Terms: obsid.f tid.f grade.f comp.f Residuals Sum of Squares 306.23399 221.38173 1.70000 14.52831 279.05780 Deg. of

Hello all, I want box plots by group to display in order of increasing mean (or median) of each group but can't seem to figure it out and couldn't find anything on R-seek, either. My data looks like this: meas unit sid grade rsprti 1 2.24 1002 99999902 NA 0.8600000 2 3.04 1007 43589520 3 0.9400000 3 4.95 2002 39910470 5 1.5300000 4 2.24 2002 39986280 5

Hello R, I am looking for non-parametric simulation in IRT. Is there any IRT package that does non-parametric simulation? helen L [[alternative HTML version deleted]]

The first version of the package plink has been uploaded to CRAN. plink is a package for conducting unidimensional IRT scaling and chain linking for multiple groups for single-format or mixed-format common items. The package supports eight IRT models and four calibration methods. Dichotomous Models: 1PL, 2PL, 3PL Polytomous Models: -Graded response model -Partial credit model -Generalized

The first version of the package plink has been uploaded to CRAN. plink is a package for conducting unidimensional IRT scaling and chain linking for multiple groups for single-format or mixed-format common items. The package supports eight IRT models and four calibration methods. Dichotomous Models: 1PL, 2PL, 3PL Polytomous Models: -Graded response model -Partial credit model -Generalized

Using the grm function (graded response IRT model) in the ltm package I receive the following error: Error: subscript out of bounds for several scales I'd like to examine. Here's a small example that if run a few times will likley produce the error at least once ch<-array(round(runif(50,1,5)),c(10,5)) grm(ch,start.val="random") ## or

hello R: we have a two-parameter IRT simulation code. The goal is to generate a response matrix.But the "for" part doesn't run. we don't know what is wrong with it. Thanks so much~~~ I <- 10 J <- 5 response <- matrix(0, 10, 5) pij <- function(a,b,theta) { a <- rnorm(J, 0.8, 0.04) a b <- rnorm(J, 0, 1) b theta <- rnorm(I, 0,1) theta for( i in 1:I ) { for(

Hello forum, I have developed an IRT model for a set of items on a large reference sample. I now want to use the IRT parameters that were estimated in the reference sample to score new individuals, one at a time. What R package(s) would allow me to do this? Also, several covariates were associated with item thresholds in the reference sample, so I was wondering if any programs can take

Hi Everybody, I have just been introduced to R and have used the ltm package for calibrating items under IRT. I have been able to get the item parameters using the fit function under different models. I am using the 2PL model. I have got the parameters for some 300 items from 15 different tests using the function fit. Now I need to automatically generate tests such that they have atleast a

Hi: I need to apply the IRT model from Ramsay (1991), He apply the Smoothing Kernel to multiple choice test. Is possible in R?. Thank you, Xavier G. Ordonez Doctoral Student Universidad Complutense de Madrid

Hi all, Could anyone tell me if there is some package that fits any Item Response Model (further the ltm package)? Regards, Caio --------------------------------- [[alternative HTML version deleted]]

Hello R: i work on an IRT simulation research. I've written a code to generate a single dataset.As i will repeat simulating the data 100 times under every condition, how can i write the R code to make it run the single simulation code 100 times and save the generate results each time? Thanks so much~