If you just want to fit the 2PL, without any covariates, then this can be currently handled by function ltm() in package ltm.
Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm ----- Original Message ----- From: "Doran, Harold" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; "R-Help" <[email protected]> Cc: <[EMAIL PROTECTED]> Sent: Monday, October 02, 2006 12:22 PM Subject: Re: [R] multilevel factor model in lmer > Dan: > > lmer cannot currently be used for the 2PL. As you note, it is > straightforward to estimate the 1PL, but the a-parameters present a > current challenge. Doug mentioned to me the other day he is doing > some work on this, so I have copied him on this reply. > > Harold > > > -----Original Message----- > From: [EMAIL PROTECTED] on behalf of Dan Powers > Sent: Sun 10/1/2006 10:15 PM > To: 'R-Help' > Subject: [R] multilevel factor model in lmer > > > Hello -- > > I am curious if lmer can be used to fit a multilevel factor model > such as a > two-parameter item response model. The one parameter model is > straightforward. A two-factor model requires a set of factor > loadings > multiplying a single random effect. For example, a logit model for > the ith > subject responding correctly to the jth item (j=1,..,J) is > > logit[p(ij)] = a1*item1(i) + ... + aJ * itemJ(i) + > lambda1*item1(i)*u(i) + ... + lambdaJ*itemJ(i)*u(i) > > where the lambdas are factor loadings, with lambda1 fixed to 1.0 and > item1-itemJ are dummy variables for the items. > > Thanks, > Dan > > =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= > Daniel A. Powers, Ph.D. > Department of Sociology > University of Texas at Austin > 1 University Station A1700 > Austin, TX 78712-0118 > phone: 512-232-6335 > fax: 512-471-1748 > [EMAIL PROTECTED] > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
