Design of Experiments Guide • Mixture Designs • The Optimal Mixture Design
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The Optimal Mixture Design
The Optimal mixture design choice invokes the custom designer with the mixture variables entered into the response and factors panels. To create an optimal mixture design:
1.
Select DOE > Mixture Design.
2.
Enter factors and responses. The steps for entering responses are outlined in Responses in Custom Designs.
3.
After you enter responses and factors, click Continue.
4.
Click Optimal on the Choose Mixture Design Type panel.
5.
Open the Define Factor Constraints node and click Add Constraint to add linear constraints, if you have any.
6.
Add effects to the model using the instructions below.
7.
In the Design Generation panel, make selections relative to blocks, center points, replicates, and the number of runs.
8.
Click Make Design to generate the Mixture Design report, which displays the design and Design Evaluation report.
9.
Click Make Table in the Output Options panel of the Mixture Design report to generate the data table.
Adding Effects to the Model
Initially, the Model panel lists only the main effects corresponding to the factors that you entered, as shown in The Model Panel.
The Model Panel
However, you can add factor interactions, specific crossed factor terms, powers, or Scheffé Cubic terms to the model.
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To add interaction terms to a model, click the Interactions button and select 2nd, 3rd, 4th, or 5th. For example, if you have factors X1 and X2, click Interactions > 2nd and X1*X2 is added to the list of model effects.
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To add crossed effects to a model, highlight the factors and effects that you want to cross and click the Cross button.
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To add powers of continuous factors to the model, click the Powers button and select 2nd, 3rd, 4th, or 5th.
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When you want a mixture model with third-degree polynomial terms, the Scheffé Cubic button provides a polynomial specification of the surface by adding terms of the form X1*X2*(X1-X2).