Re: [R] multilevel factor model in lmer

From: Dan Powers <dpowers_at_mail.la.utexas.edu>
Date: Mon 02 Oct 2006 - 15:55:04 GMT


Harold and Dimitris --
Thanks very much.
Cheers,
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
dpowers@mail.la.utexas.edu

-----Original Message-----
From: Dimitris Rizopoulos [mailto:dimitris.rizopoulos@med.kuleuven.be] Sent: Monday, October 02, 2006 6:05 AM
To: Doran, Harold; dpowers@mail.la.utexas.edu; R-Help Cc: dmbates@gmail.com
Subject: Re: [R] multilevel factor model in lmer

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


> 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: r-help-bounces@stat.math.ethz.ch 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
> dpowers@mail.la.utexas.edu
>
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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. Received on Tue Oct 03 01:59:09 2006

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