Salt Amount Salt Rating Responses no salt 1, 3, 2, 4, 2, 2, 1, 4, 3, 4 1 tsp. 4, 5, 3, 4, 5, 4, 5, 5, 4, 5 2 tsp. 4, 3, 5, 1, 4, 2, 5, 4, 3, 2 3 tsp. 3, 1, 2, 3, 1, 2, 1, 2, 1, 2
 1 Select Help > Sample Data Library and open Salt in Popcorn.jmp.
 2 Select Analyze > Fit Model.
 3 Select Taste Test from the Select Columns list and click Y.
 4 Select Salt from the Select Columns list and click Macros > Response Surface.
 5 Click Run.
 6 Click the disclosure icon next to Response Surface to open the report.
Ordinal Logistic Fit for Salt in Popcorn.jmp
The report shows how the quadratic model fits the response probabilities. The curves, instead of being shifted logistic curves, become stacked U-shaped curves where each curve achieves its minimum at the same point. The critical value is at Mean(X)–0.5 * (b1/b2) where b1 is the linear coefficient and b2 is the quadratic coefficient. This formula is for centered X. From the Parameter Estimates table, you can compute that the optimal amount of salt is 1.5 - 0.5 * (0.5637/1.3499) = 1.29 teaspoons.
The parameter estimates for Salt and Salt*Salt are the coefficients used to find the critical value. Although the critical value appears on the logistic plot as a minimum, it is 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 Ordinal Logistic Fit for Salt in Popcorn.jmp, where 1.29 is shown under Critical Value.

Help created on 9/19/2017