The function factor.scores is used with package ltm and others to estimate IRT type scores for various models.  It inherits objects of class grm, gpcm and a few others.  What I would like to do is to use the factor.scores function, but feed it my own item parameters (from a bifactor model where the 2PL parameters are adjusted for the bifactor structure). Does anybody have an idea of how this might be done?  I can, of course, create a list, matrix or other object containing the item parameters, but factor.scores only inherits particular object classes.  Any thoughts would be great. Thanks,

Jimmy

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