Modeling and Multivariate Methods - SAS

Chapter 7 Performing Logistic Regression on Nominal and Ordinal Responses 225
Example of a Quadratic Ordinal Logistic Model
Figure 7.25 Ordinal Logistic Fit for Salt in Popcorn.jmp
The distance between each curve measures the probability of each of the five response levels. The probability
for the highest response level is the distance from the top curve to the top of the plot rectangle. This distance
reaches a maximum when the amount of salt is about 1.3 teaspoons. All curves share the same critical point.
The parameter estimates for Salt and Salt*Salt become the coefficients used to find the critical value.
Although it appears as a minimum, it is only a minimum with respect to the probability curves. It is really a
maximum in the sense of maximizing the probability of the highest response. The Solution portion of the
report is shown under Response Surface in Figure 7.25, where 1.29 is shown under Critical Value.