The Power of Foldover Designs

Music City Center 

The analysis of screening designs is often based on a second-order model with linear main effects, two-factor interactions, and quadratic effects. When the main effect columns are orthogonal to all the second-order terms, a two-stage analysis may be conducted starting with fitting a main effect only model. A popular technique to achieve this orthogonality is to take any design and append its foldover runs. In this talk, we show that this foldover technique is even powerful than originally thought because it also includes opportunities for unbiased estimation of the variance either by pure error or lack of fit. We find optimal foldover designs for main effect estimation and other designs that balance main effect estimation and model selection for the important factors. A real life implementation of our new designs involving 8 factors and 20 runs is discussed.

Optimal design

Response surface design

Experimental design 

Section on Physical and Engineering Sciences