[R] multilevel factor model in lmer

[Dan Powers]

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 at mail.la.utexas.edu