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.
