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:
Select Help > Sample Data Library and open
Select Analyze > Fit Y by X.
Select Response and click Y, Response.
Select In(Dose) and click X, Factor.
Notice that JMP automatically fills in Count for Freq. Count was previously assigned the role of Freq.
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.
Example of Crosshair Tool on Logistic Plot

Help created on 9/19/2017