Re: [R] multilevel factor model in lmer

From: Doran, Harold <HDoran_at_air.org>
Date: Mon 02 Oct 2006 - 10:22:43 GMT

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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