Example of a Simplex Centroid Design
main topic     interpreting results     session command     see also 

Suppose you want to study how the proportions of three ingredients in an herbal blend household deodorizer affect the acceptance of the product based on scent. The three components are neroli oil, rose oil, and tangerine oil.

1    Choose Stat > DOE > Mixture > Create Mixture Design.

2    Under Type of Design, choose Simplex centroid.

3    From Number of components, choose 3.

4    Click Designs. Make sure Augment the design with axial points is checked. Click OK.

5    Click Components. In Name, enter Neroli, Rose, and Tangerine in rows 1 to 3, respectively. Click OK.

6    Click Results. Choose Detailed description and design table.

7    Click OK in each dialog box.

Session window output

Simplex Centroid Design

 

 

Components:         3  Design points:  10

Process variables:  0  Design degree:   3

 

Mixture total: 1.00000

 

 

Number of Boundaries for Each Dimension

 

Point Type  1  2  0

Dimension   0  1  2

Number      3  3  1

 

 

Number of Design Points for Each Type

 

Point Type    1  2  3  0  -1

Distinct      3  3  0  1   3

Replicates    1  1  0  1   1

Total number  3  3  0  1   3

 

 

Bounds of Mixture Components

 

          Amount        Proportion    Pseudocomponent

Comp   Lower   Upper   Lower   Upper   Lower    Upper

A     0.0000  1.0000  0.0000  1.0000  0.0000   1.0000

B     0.0000  1.0000  0.0000  1.0000  0.0000   1.0000

C     0.0000  1.0000  0.0000  1.0000  0.0000   1.0000

 

 

Design Table (randomized)

 

Run  Type       A       B       C

  1     1  0.0000  1.0000  0.0000

  2    -1  0.1667  0.6667  0.1667

  3     2  0.5000  0.5000  0.0000

  4     1  1.0000  0.0000  0.0000

  5     1  0.0000  0.0000  1.0000

  6     2  0.5000  0.0000  0.5000

  7     0  0.3333  0.3333  0.3333

  8    -1  0.6667  0.1667  0.1667

  9     2  0.0000  0.5000  0.5000

 10    -1  0.1667  0.1667  0.6667

Interpreting the results

Minitab creates an augmented three-component simplex centroid design. The base design provides seven runs; augmentation adds three runs for a total of ten runs.

Because you chose to display the detailed description and data tables, Minitab shows the component proportions you will use to create ten blends of your mixture. When you perform the experiment, use the blends in the run order that is shown. (Because you did not change the mixture total from the default of one, Minitab expresses each component in proportions.) For example, the first blend you will test will be made up of only rose oil: neroli (0.0000), rose oil (1.0000), and tangerine oil (0.0000).

Note

Minitab randomizes the design by default, so if you try to replicate this example, your run order may not match the order shown.