Design and Analysis of Experiments by Douglas Montgomery. Heath Rushing

would also be possible to create an additional column in the data table that contains the transformed values. An advantage of using the transform option, however, is that the predicted values from the Fit Model report are automatically transformed back to the original scale for prediction.

      12. Click Run.

      The Residual by Predicted Plot for the ANOVA of the transformed response does not show the same increasing “funnel” of variance that appears in the plot for the analysis of the original response.

      13. Select Window > Close All.

      Example 3.7 Tukey Multiple Comparisons

      NOTE: It is possible to perform the multiple comparisons procedures of the next three examples either using the Fit Y by X platform or the Fit Model platform. The next three examples use Fit Y by X, and the example labeled Section 3.8.2 uses Fit Model.

      1. Open Etch-Rate.jmp.

      2. Select Analyze > Fit Y by X.

      3. Select Etch Rate and select Y, Response.

      4. Click Power and select X, Factor.

      5. Click OK.

      6. Click the red arrow next to One-way Analysis of Etch Rate By Power and select Compare Means > All Pairs, Tukey HSD.

      The LSD (least significant difference) Threshold Matrix reports positive values in components that correspond to significantly different pairs of treatment effects. This information is summarized in the Connecting Letters Report. The Ordered Differences Report lists the pairwise comparisons according to magnitude of the difference between the treatment means. The Tukey procedure indicates that all pairs of means are significantly different.

      7. Leave the Fit Y by X report open for the next two examples.

      Example 3.8 Fisher Multiple Comparison

      1. Return to the Fit Y by X platform from the previous example.

      2. Click the red arrow next to One-way Analysis of Etch Rate By Power and select Compare Means > Each Pair, Student’s t.

      The interpretation of this report is the same as it was for Tukey’s test. However, this procedure does not control for the experimentwise error rate. Notice how the confidence intervals for the differences between treatment means are smaller when created using the Fisher Multiple Comparison method than the same intervals that are created when using Tukey’s method.

      3. Leave the Fit Y by X report open for the next example.

      Example 3.9 Dunnett’s Multiple Comparison

      1. Return to the Fit Y by X platform from the previous example.