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Publication date: 07/30/2020

Comparison with a Fractional Factorial Design

Suppose that you had chosen a traditional screening design instead of the definitive screening design in Definitive Screening Design. This example compares the two designs in terms of confounding.

1. Select DOE > Classical > Two Level Screening > Screening Design.

2. Double-click Y under Response Name and type Yield.

3. Select Help > Sample Data Library and open Design Experiment/Extraction

4. Click the red triangle next to and select Load Factors.

The factor names and ranges are added to the Factors outline.

5. Click Continue.

6. Select Choose from a list of fractional factorial designs.

7. Click Continue.

Potential designs appear in the Design List.

Figure 7.6 Screening Design List for Six Continuous Factors 

8. Select the sixteen-run fractional factorial design with no blocks, shown highlighted in Figure 7.6.

9. Click Continue.

10. Open the Display and Modify Design > Aliasing of Effects outline.

Figure 7.7 Aliasing of Effects for Fractional Factorial Design 

The Aliasing of Effects outline for the 16-run fractional factorial design shows that every two-factor interaction is confounded with at least one other two-factor interaction. In this fractional factorial design, the Ethanol*Time interaction is confounded with Methanol*pH. To determine which interaction is active, you need to run additional trials. If the factors had been entered in a different order, the Ethanol*Time interaction might have been aliased with two other two-factor interactions.

In the section Definitive Screening Design, you constructed a 17-run definitive screening design. The Color Map on Correlations for this DSD (Figure 7.4) shows that no two-factor interactions are confounded with any other two-factor interactions. For the fractional factorial design, there are seven instances of confounded two-factor interactions. If you suspect that there are active two-factor effects, the DSD is the better choice.

You can conduct a more thorough comparison of the two designs using the Compare Designs platform (DOE > Design Diagnostics > Compare Designs). See Compare Designs.

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