# Regular Two-Level Factorial Designs

The Regular Two-Level Factorial Design Builder offers two-level full factorial and regular fractional factorial designs. You can investigate 2 to 21 factors using 4 to 512 runs. This collection of designs provides an effective means for screening through many factors to find the critical few.

Full two-level factorial designs may be run for up to 9 factors. These designs permit estimation of all main effects and all interaction effects (except those confounded with blocks.)

Stat-Ease offers a wide variety of fractional factorial designs. Detailed information about the alias structure is calculated when the design is built. This evaluation should be inspected to ensure the selected design can cleanly estimate the interactions of interest.

Replicates: The value in this box is the number of times the requested design will be produced. The number of runs in the final design is the number of replicates times the number of runs in the requested base design.

We do not recommend replicating a fractional factorial design.

Blocks: The value in this box is the number of pieces to break the design into to account for known sources of variation. See blocking for more information.

When the number of blocks equals the number of replicates. The replicated designs will be in their own blocks.

Center points per block: When there are numeric factors, center points can be added to check for curvature. The number entered here will be the number of center points randomized within each block.

Show Generators: Checking this box brings up the advanced generators interface when Next is clicked.

The roman numerals on this screen are the resolution. They are also color coded such that no color is a full factorial, red are Resolution III, yellow are resolution IV, and green are at least resolution V.

Red means Stop and Think: A resolution III design indicates that main effects may be aliased with two factor interactions. Resolution III designs can be misleading when significant two-factor interactions affect the response.

Yellow means Proceed with Caution: A resolution IV design indicates that main effects may be aliased with three-factor interactions. Two-factor interactions may be aliased with other two-factor interactions. Resolution IV designs are a good choice for a screening design because the main effects will be clear of two-factor interactions.

Green means Go Ahead: Resolution V (or higher) designs are just about as good as a full factorial, while saving some runs. There is an assumption that main effects and two-factor interactions can adequately model the response surface.