I ran a negative binomial model to predict an ordered outcome with 6 levels and a large (2/3 of sample) number of zero values. Measured variable values ranged from 0 through 5. The output reported that a value of the criterion variable had to be fixed at its extreme, which was 15, but also that the model terminated normally. Three questions: what does this mean? Is there something to fix in the data and how? And, can I trust the output? Thank you.
You say "negative binomial" and also "an ordered outcome". They wouldn't be one and the same because negbin is for count outcomes. Perhaps you mean that the count variable predicts an ordinal outcome but that isn't clear. You may want to send your output to Support along with your license number.