Follow-up designs to resolve confounding in split-plot experiments

Ashraf A. Almimi, Murat Kulahci, Douglas Montgomery

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Split-plot designs are effective in industry due to time and/or cost constraints, restriction on randomization of the treatment combinations of the hard-to-change factors, and different sizes of experimental units. Some of the results of fractional factorial split-plot experiments can be ambiguous and a need may arise to conduct follow-up experiments to separate effects of potential interest by breaking their alias links with others. For completely randomized fractional factorial experiments, methods have been developed to construct follow-up experiments. In this article, we extend the foldover technique to break the alias chains of split-plot experiments. Because it is impractical or not economically possible to foldover the whole-plot factors, as their levels are often hard or expensive to change, the focus of this article is on folding over only one or more subplot factors in order to de-alias certain effects. Six rules are provided to develop foldovers for minimum aberration resolution III and resolution IV fractional factorial split-plot designs.

Original languageEnglish (US)
Pages (from-to)154-166
Number of pages13
JournalJournal of Quality Technology
Issue number2
StatePublished - Apr 2008


  • Alias
  • Foldover design
  • Minimum aberration
  • Reduced defining relation
  • Resolution III designs
  • Resolution IV designs
  • Split-plot design

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Strategy and Management
  • Management Science and Operations Research
  • Industrial and Manufacturing Engineering


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