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Specify the design for Create Mixture Design (Extreme Vertices)

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Stat > DOE > Mixture > Create Mixture Design > Designs

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Degree of design

Select the type of blends to include in the design and how many different settings to use for each type of blend. The higher the degree, the more complex the model the design can fit. The following table shows simplex designs of varying degrees with four component designs. The number of blends become more complicated with extreme vertices designs.
Degree Number of blends
1 Contains only vertex points.
2 Contains double blends where the components are mixed equally.
3 Two double blends for each pair of components and triple blends that are mixed equally.
4 Three double blends for each pair of components and two triple blends for each trio of components.
For more information about the types of models up to degree 3, go to What is the degree of a lattice?.

Augment the design with center point

Select this option to include a point in the center of the design space. Center points have multiple uses. Designs with process variables or replicates increase the number of center points in the final design. For more information on augmentation, go to How Minitab augments mixtures designs by adding center points.

Augment the design with axial points

Select this option to include 1 axial point per component in the base design. An axial point is a blend where the component proportions are the average of the center point and a vertex. A design with these interior points provides more information about the inner portion of the response surface to model more complicated curvature. For diagrams that show examples of unaugmented and augmented simplex designs with three components, go to Choose a mixture design.

Replicate Design Points

Specify how many times to perform each experimental run that is in the base design. Usually, you consider the available resources and the purpose of your design when you select the number of replicates. You can add replicates to your design later with Stat > DOE > Modify Design. For more information on replicates, go to Replicates and repeats in designed experiments.
  • Number of replicates for the whole design: Select the number of replicates for all of the points in the design. Replicates are multiple experimental runs with the same component settings. (If the design has process variables, these settings are the same too.) Usually, you consider the available resources and the purpose of your design when you choose the number of replicates.
  • Number of replicates for the selected types of points: Select this option to replicate some types of points in the design instead of all points. For example, you can replicate center points to estimate pure error when you do not have enough resources to replicate other types of points. The Point Type column shows the value that identifies that type of point when you store the design in the worksheet. Enter the number of replicates for each point type in the Number column.
    vertex
    Points where each component is at one of its boundaries or constraints. In a base design without linear constraints, the number of vertex points is the same as the number of components.
    blends
    Point on the edge or face of the design space defined by two or more vertices. Points with at least one component proportion set to 0. For example, a double blend has two non-zero component proportions and 0 for any other component proportions. A triple blend has 3 non-zero component proportions and 0 for any other component proportions.
    Note

    For simplex lattice designs and extreme vertices designs, replication of blend points adds experimental runs only if the degree of the design includes the blend in the base design.

    center point
    Points that is at the center of the design space. The base design has 1 center point.
    axial point
    Points whose component proportions are averages of the proportions of the center point and a vertex. Axial points have no component proportions set to 0. In the base design, the number of axial points is the same as the number of vertex points. Replication of these points adds experimental runs only if you selected to augment the design with axial points.
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