When doing estimation of item factor analysis models in OpenMx, I'm wondering if there's a way to override the lower boundary on the item slopes (currently 1e-6, I think) for the dichotomous and graded item response models. e.g., imagine one wants to fit a multidimensional model, perhaps w/ crossloadings, or one has reverse worded items and it is expected that some item slopes will go negative. I believe these bounds may be set in the rpf package as rpf.ParamInfo returns this lower bound for the rpf.drm and rpf.grm item models. Currently when attempting to fit such a model I get an error such as:
Error in runHelper(model, frontendStart, intervals, silent, suppressWarnings, :
Starting value const.item[1,1] -1.000000 less than lower bound 0.000001
If you need code to reproduce this, I understand, let me know.
Many thanks!