Basic Analysis and Graphing - SAS

232 Performing Simple Logistic Regression Chapter 7
Additional Examples of Logistic Regression
8. Move the cross-hair intersection to the prediction line, and read the In(dose) value that shows on the
horizontal axis.
In this example, a rabbit with a In(dose) of approximately -0.9 is equally likely to be cured as it is to die.
Figure 7.10 Example of Crosshair Tool on Logistic Plot
Example of Inverse Prediction Using the Inverse Prediction Option
If your response has exactly two levels, the Inverse Prediction option enables you to request an exact inverse
prediction. You are given the x value corresponding to a given probability of the lower response category, as
well as a confidence interval for that x value.
To use the Inverse Prediction option, proceed as follows:
1. Open the Penicillin.jmp sample data table.
2. Select Analyze > Fit Y by X.
3. Select Response and click Y, Response.
4. Select In(Dose) and click X, Factor.
Notice that JMP automatically fills in Count for Freq. Count was previously assigned the role of Freq.
5. Click OK.
6. From the red triangle menu, select Inverse Prediction. See Figure 7.11.
7. Type 0.95 for the Confidence Level.
8. Select Two sided for the confidence interval.
9. Request the response probability of interest. Type 0.5 and 0.9 for this example, which indicates you are
requesting the values for ln(Dose) that correspond to a 0.5 and 0.9 probability of being cured.
10. Click OK.
The Inverse Prediction plot appears.