Comparison of two generalized logistic regression models; a case study

Two generalized logistic regression models were compared on a set of observations describing persons with mental disabilities. The main variable of interest (willingness of the parents to incorporate their mentally handicapped offspring into on-farm activities) has three different values (no, undecided, yes). These values can be regarded as unordered (the variable having nominal measurement scale) or as ordered (the variable having ordinal measurement scale). Nominal and ordinal logistic regression models were used to analyze the impact of several predictors on the main variable of interest. We compare the two models in terms of the likelihood ratio test and the Nagelkerke coefficient of determination. It turns out that the ordinal regression assumptions are often not met. In our case, the nominal regression model has proved preferable to the ordinal regression one.