How are ordered categories handled?
The basic LCA model does not distinguish between unordered categorical (nominal) and ordered categorical data. For ordered category data, one may wish to supply additional constraints to the model. These constraints (1) reduce the number of parameters that require estimation and (2) insure that results will have a form consistent with the known ordering of response levels. Clogg (1979) showed how simple equality constraints can be used to accommodate ordered-category or Likert-type data. Other systems of structural constraints, based on logistic (Rost, 1985, 1988) or probit (Uebersax, 1993) models are also available.
