SUBJECT: Some of the predicted categories missing in the ordinal logistic regression output
In my ordinal logistic regression model, I have a set of 7 inputs and I have Y = 2, 3, 4, ..., 19 (18 categories) as my response variable. I use
SAS PROC LOGISTIC and I am using the output probabilities to classify each observation in to a specific category depending on which probability of the 18 probabilities output by SAS is the maximum. For example, if p10 is the highest probability of all 18 probabilities, then, I classify this observation in to category 10. Just to double check, I also use the estimates output by
proc logistic and do explicit logistic calculations as follows:
cum prob, c1 = exp(&inter1 - modelScore)/(1 + exp(&inter1 - modelScore)) ... cum prob, c17 = exp(&inter17 - modelScore)/(1 + exp(&inter17 - modelScore));
and calculate the individual probabilities p1 to p18 with
p1 = c1,
p2 = c2 - p1, and
p18 = 1 - c17.
The problem is, the categories (2, 3, 6, 7, 9, 10, 16, 18) are never occurring in the predicted response. Can someone explain to me what I might be doing wrong? Whether I use SAS probabilities or the explicitly calculated probabilities, the same rating categories are missing in the predicted response although the Y response variable has the entire spectrum from 2 to 18.