lack-of-fit-test is missing

[#1]

Hello.

I have created a full factorial design with two X variables and one response value (Health as a function of your drinking and smoking habits, see enclosed files).

When I generate the report, the lack-of-fit test is greyed out. But why? The fitting-linear-models-pdf from the jmp-help says:

In the following situations, the Lack of Fit report does not appear because the test statistic

cannot be computed:

• There are no replicated points with respect to the X variables, so it is impossible to

calculate a pure error sum of squares.

• The model is saturated, meaning that there are as many estimated parameters as there are

observations. Such a model fits perfectly, so it is impossible to assess lack of fit.

I have 3 replicated points for every X variable and 27 observations which is a greater number than the estimated parameters. So why can't I compute the LoF-test?

[#2 · Accepted solution]

If you run a Stepwise Regression instead of the Standard Least Squares you will get the Lack of Fit statistic.