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Note: Use the Add Blocks without Extra Center Runs option only if you can assume that not all quadratic effects are important.
If a design contains a categorical factor, a center run is a run where all continuous factors are set at their middle values. If all factors are categorical, the two blocking options are available. Both options produce designs whose blocks are orthogonal to main effects.
Note: For details about the construction and properties of blocked designs that estimate quadratic effects, see Jones and Nachtsheim (2016). The paper also contains information about treating the blocks as random effects.
The Add Blocks with Center Runs to Estimate Quadratic Effects option constructs a design with these properties:
If a design contains only continuous factors, a blocked design for k factors having these properties can be constructed as follows:
When some factors are categorical, the Add Blocks with Center Runs to Estimate Quadratic Effects option adds pairs of center runs within certain blocks. This structure ensures orthogonality and the ability to estimate all main and quadratic effects.
The Add Blocks without Extra Center Runs option constructs a design that has a single center run when all factors are continuous and two center runs when some factors are categorical. The resulting design has these properties:
A blocked design for k factors without extra center runs is constructed as follows:

Help created on 3/19/2020