I'm new to 'R', so forgive me if I've used the wrong term. I'd like to model some Likert-style items using Rasch methods. I've been unable to find mention of these for 'R'. Would someone happen to know of any? Thanks in any case. Bill ------------ "It is the time that you have wasted for your rose that makes your rose so important."--St-Exupery -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
On 07/12/02 11:00, Bill Bell wrote:> >I'm new to 'R', so forgive me if I've used the wrong term. > >I'd like to model some Likert-style items using Rasch methods. > >I've been unable to find mention of these for 'R'. Would someone happen to >know of any?I once fit some data using a Rasch-type model with nls in the nls library, using commands roughly like: logit <- function(x) {exp(x)/(1+exp(x))} icc.tmp<-nls(score~C*logit((mscore-A)/B)+D) start=list(A=astart[i],B=.1,C=.5,D=.5), control=nls.control(tol=.025)) These were not Likert-type items but test items that were scored as correct or incorrect. The model would be more complicated with several different cutoffs, and I don't want to take the time to figure out how to do it. It is similar to Thurstone category scaling, I assume. I note that the data I had were very messy, and the model fit poorly and often failed to converge at all. If I did this again I would either make sure I had better data or else I would use optim() (in the base package) instead of nls, or both. Note also that various Rasch models allow you to specify various parameters, such as an upper bound, lower bound, midpoint, and slope. -- Jonathan Baron, Professor of Psychology, University of Pennsylvania Home page: http://www.sas.upenn.edu/~baron R page: http://finzi.psych.upenn.edu/ -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Bill, A colleague and I are working on a project that would offer both Rasch and IRT item parameters estimation along with fit statistics. Additionally, I wrote S/R code to produce all classical test theory (true score model) statistics. The project is somewhat in its infancy but you can find the C++ code and some initial code files on sourceforge and CVS repositories. We are both extremely busy so progress has been slow. If you have any programming expertise in R, we would encourage you to contribute to the project where you can. Please find the project at the following URL: http://sourceforge.net/projects/ssm/ Cheers, Patrick --- Bill Bell Wrote: I'm new to 'R', so forgive me if I've used the wrong term. I'd like to model some Likert-style items using Rasch methods. I've been unable to find mention of these for 'R'. Would someone happen to know of any? Thanks in any case. Bill -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._