Basic Analysis and Graphing - SAS

Chapter 7 Performing Simple Logistic Regression 231
Additional Examples of Logistic Regression
Figure 7.9 Examples of ROC Curve and Table
Since the ROC curve is well above a diagonal line, you conclude that the model has good predictive ability.
Example of Inverse Prediction Using the Crosshair Tool
In a study of rabbits who were given penicillin, you want to know what dose of penicillin results in a 0.5
probability of curing a rabbit. In this case, the inverse prediction for 0.5 is called the ED50, the effective
dose corresponding to a 50% survival rate. Use the crosshair tool to visually approximate an inverse
prediction.
To see which value of In(dose) is equally likely either to cure or to be lethal, 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. Click on the crosshairs tool.
7. Place the horizontal crosshair line at about 0.5 on the vertical (Response) probability axis.