Choose a mixture design

Before you use Minitab, you need to determine what design is most appropriate for your experiment. Minitab provides simplex centroid, simplex lattice, and extreme vertices designs.

When you are choosing a design you need to do the following steps:

  1. Identify the components, process variables, and mixture amounts that are of interest.
  2. Determine the model that you want to fit.
  3. Ensure adequate coverage of the experimental region of interest.
  4. Determine the impact that other considerations have on your choice of a design. Examples of other considerations include cost, time, availability of facilities, and lower and upper bound constraints.

Examples of mixtures designs that you can create

To help you visualize a mixture design, the following figures show design points using triangular coordinates. Each point on the triangle represents a specific blend of components that you would use in your experiment. For simplicity, the figures show three component designs. The following diagrams only show a few of the mixture designs you can create. Minitab can also create simplex lattice designs up to degree 10 and extreme vertices designs.

  Unaugmented Augmented
Simplex Centroid

You can fit up to a special cubic model.

You can partially fit up to a special cubic model.

Simplex Lattice Degree 1

You can fit a linear model.

You can partially fit up to a quadratic model.

Simplex Lattice Degree 2

You can fit up to a quadratic model.

You can partially fit up to a special cubic model.

Simplex Lattice Degree 3

You can fit up to a full cubic model.

You can fit up to a full cubic model.

Note

When selecting a design, it is important to consider the maximum order of the fitted model required to adequately model the response surface. Mixture experiments frequently require a higher-order model than is initially planned. Therefore, when possible, conduct additional runs beyond the minimum required to fit the model.

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