Latent Class Item Response Theory (LC-IRT) Models under Within-Item Multidimensionality R package MLCIRTwithin version 2.1.2 CRAN Task View: MissingData (https://CRAN.R-project.org/view=MissingData) CRAN Task View: Psychometrics (https://CRAN.R-project.org/view=Psychometrics) Framework for the Item Response Theory analysis of dichotomous and ordinal polytomous outcomes under the assumption of within-item multidimensionality and discreteness of the latent traits. The fitting algorithms allow for missing responses and for different item parametrizations and are based on the Expectation-Maximization paradigm. Individual covariates affecting the class weights may be included in the new version together with possibility of constraints on all model parameters. Software Depends: R (>= 2.0.0), MASS, limSolve, MultiLCIRT Francesco Bartolucci <francesco.bartolucci@unipg.it> Comprehensive R Archive Network (CRAN) Francesco Bartolucci [aut, cre], Silvia Bacci [aut] GPL (>= 2) 2025-06-28 application/tgz https://CRAN.R-project.org/package=MLCIRTwithin doi:10.32614/CRAN.package.MLCIRTwithin