hi, is there a way to estimate the parameters of an IRT model (in my case, the graded response model), when some item parameter are already known? what i have heard is that other irt programs such as parscale allow to prespecify some of the item difficulty and location parameters and estimate only the unconstrained parameters. i usually use ltm for model estimation. best, felix Dr. rer. nat. Felix Fischer Diplom-Psychologe Institut f?r Sozialmedizin, Epidemiologie und Gesundheits?konomie Charit? - Universit?tsmedizin Berlin Luisenstrasse 57 10117 Berlin Tel: 030 450 529 104 Fax: 030 450 529 902 http://epidemiologie.charite.de