Testing multiple dispersion effects in unreplicated fractional factorial designs

Richard N. McGrath, Dennis K.J. Lin

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


In unreplicated 2k-p designs, the assumption of constant variance is commonly made. When the variance of the response differs between the two levels of a column in the effect matrix, that column produces a dispersion effect. In this article we show that two active dispersion effects may create a spurious dispersion effect in their interaction column. Most existing methods of dispersion-effect testing in unreplicated fractional designs are subject to these spurious effects. We propose a method of dispersion-effect testing based on geometric means of residual sample variance. We show through examples from the literature and simulations that the proposed test has many desirable properties that are lacking in other tests.

Original languageEnglish (US)
Pages (from-to)406-414
Number of pages9
Issue number4
StatePublished - Nov 2001

All Science Journal Classification (ASJC) codes

  • Statistics and Probability
  • Modeling and Simulation
  • Applied Mathematics


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