What does it mean that the model has an identification problem?
In order for parameter estimation to proceed properly, there must be enough independent information available from data to produce the parameter estimates. Identification problems tend to occur under the following conditions: a lot of parameters are being estimated; the sample size is small in relation to the maximum possible number of response patterns; or the rho parameters are close to 1/number of response categories rather than closer to zero or one. Often, adding reasonable parameter restrictions in order to reduce the number of parameters being estimated will help to achieve an identified model.
