I am conducting a regression. There is an ordinal dependent variable (ordered from 1 to three) and some categorical independent variables (each of them includes several items).
I adopted the multilevel mixed-effects ordered logistic regression using
stata software. Unfortunately, the regression outputted regression's results with omitting the results of last item of each categorical variable and showing that there is a collinearity between the items.
Is there anybody encountered the same problem? what should I do on this?