Note: Use the Add Blocks without Extra Center Runs option only if you can assume that not all quadratic effects are important.
 • Add Blocks without Extra Center Runs
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.
The Add Blocks with Center Runs to Estimate Quadratic Effects option constructs a design with these properties:
 • Block effects are orthogonal to main effects.
 • The model consisting of all main and quadratic effects is estimable.
If a design contains only continuous factors, a blocked design for k factors having these properties can be constructed as follows:
 •
 • Assign conference matrix foldover pairs to the same block.
 • Add one center run to each block.
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:
 • Block effects are orthogonal to main effects.
 •
A blocked design for k factors without extra center runs is constructed as follows:
 • Assign conference matrix foldover pairs to the same block.
 • If all factors are continuous, assign the single center run to a single block.
 • If there are categorical factors, the unblocked definitive screening design requires the addition of two center runs to the foldover pairs defined by the conference matrix. See Conference Matrices and the Number of Runs. To construct the blocked design without extra center runs, these two center runs are added to a single block.

Help created on 9/19/2017