General FAQs

How do I create a design with a continuous factor that has more than 2 levels?

There are two different approaches that a user can take to create a continuous factor with more than 2 levels.

Select Custom Design from the DOE menu.
Add all of your factors including the multi-level continuous factor(s).
Click Continue.
Select powers 2,3,(4) if necessary to form effects in model. Adding power terms will add more levels to your continuous factor. For 3 levels, add the second power.
Under Design Generation, enter the number of runs.
Click on Make design. Do not worry if there are design points at which you can not run the design.
Inspect the Variance Prediction.
Select Make Table.
For designs where you want to specify the levels of the continous factor, change them in the data table.
Select Augment Design from the DOE menu.
Identify the Xs and Identify Y.
Click Augment.
Enter the Number of Runs.
Select Make Design.
Examine the Variance Prediction.

Note: This approach is optimal to some models, just not to the original design.

Specify the continuous factor as a categorical factor with the appropriate number of levels.
Change the values of L1--LN to the values you desire.
Select Make Design.
Select Make Table.
In the data table, change the role from categorical to continuous, nominal to numeric, and remove the design role property.
Select Augment Design from the DOE menu.
Identify X factors and Identify Y factors.
Select Augment.
Build power terms in the model.
Select Make Design.
Examine the Prediction Variance.

FAQ # 2116
Last Updated: 2007 Oct 16

919.677.8008 (US)