DOE Simplified, 3rd Edition

Chapter 11

Split-Plot Designs to Accommodate Hard-to-Change Factors

Oftentimes, complete randomization of all test parameters is extremely inefficient, or even totally impractical.

Alex Sewell

53rd Test Management Group, 28th Test and Evaluation Squadron, Eglin Air Force Base

Researchers often set up experiments with the best intentions of running them in random order, but they find that a given factor, such as temperature, cannot be easily changed, or, if so, only at too much expense in terms of time or materials. In this case, the best test plan might very well be the split-plot design. A split plot accommodates both hard-to-change (HTC) factors, e.g., the cavities in a molding process, and those that are easy to change (ETC); in this case, ...