[R] DIF Analysis starting from a gpcm class object

such a thing by myself? and if so, how can I extract what I need from the model object? thanks to everybody /federico ----- Dr. Federico Andreis Università degli Studi di Milano-Bicocca, PhD Student MEB Department, Karolinska Institutet, Stockholm, Visit

[R] Multilevel IRT Modelling

Dear All, does anybody know of a package (working under Linux) for multilevel IRT modelling? I'd love to do this without having to go on WINSTEPS or the like.. thanks for the attention! Federico Andreis ----- Dr. Federico Andreis Università degli Studi di Milano-Bicocca, PhD Studen

[R] Likelihood Optimization With Categorical Variables

Dear all, I have the following problem: I have been using the routine "optim" in order to maximize a joint likelihood (basically a mixture with modeled weights) with quantitative variables..so far so good. Now I need to plug into the model a categorical variable (namely, age classes). Obviousl