Example Using Loglinear Variance

The data table InjectionMolding.jmp contains the experimental results from a 7-factor 27-3 fractional factorial design with four added centerpoints (Montgomery 1991). Preliminary investigation determined that the mean response only seemed to vary with the first two factors, Mold Temperature, and Screw Speed, and the variance seemed to be affected by Holding Time.

Figure 10.1 Injection Molding Data 

1. Select Help > Sample Data Library and open InjectionMolding.jmp.

2. Select Analyze > Fit Model.

Since the variables in the data table have been assigned preselected roles, the analysis runs automatically.

Figure 10.2 Loglinear Variance Report Window 

The Mean Model for Shrinkage report gives the parameters for the mean model, and the Variance Model for Shrinkage report gives the parameters for the variance model.