Determine the number of terms in a saturated 2-level factorial or a saturated Plackett-Burman design

Unless you choose to omit terms from your model, Minitab's power calculations are based on a model that uses all the available degrees of freedom, also known as a saturated model. Use the following table to determine the number of terms in the saturated model for a 2-level factorial design with no blocks.

You cannot perform power and sample size calculations on the saturated model unless you have center points or replicates.

Model Number of terms in the saturated model
Without center points or blocks Equals the number of unique corner points in base design - 1
Includes center points but no blocks Equals the number of unique corner points in base design

When the model contains blocks, the number of terms in the saturated model depends on the number of degrees of freedom (df) remaining after explaining blocks (df = number of blocks - 1) and center points (1 df).

The simplest way to determine the number of terms in the saturated model is to create the design and count the number of terms in the resulting model as follows:

  1. Choose Stat > DOE > Factorial > Create Factorial Design and create your design.
  2. Go to the Session window and count the number of terms displayed in the Alias Structure. Do not count the identity term (I).
    • If you have no center points, then this is the number of terms in the saturated model for the design you created.
    • If you have one or more center points, then the number of terms in the saturated model is 1 greater than this.
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