Sample size determinations for Welch's test in one-way heteroscedastic ANOVA

Show Li Jan, Gwowen Shieh*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


For one-way fixed effects ANOVA, it is well known that the conventional F test of the equality of means is not robust to unequal variances, and numerous methods have been proposed for dealing with heteroscedasticity. On the basis of extensive empirical evidence of Type I error control and power performance, Welch's procedure is frequently recommended as the major alternative to the ANOVA F test under variance heterogeneity. To enhance its practical usefulness, this paper considers an important aspect of Welch's method in determining the sample size necessary to achieve a given power. Simulation studies are conducted to compare two approximate power functions of Welch's test for their accuracy in sample size calculations over a wide variety of model configurations with heteroscedastic structures. The numerical investigations show that Levy's (1978a) approach is clearly more accurate than the formula of Luh and Guo (2011) for the range of model specifications considered here. Accordingly, computer programs are provided to implement the technique recommended by Levy for power calculation and sample size determination within the context of the one-way heteroscedastic ANOVA model.

Original languageEnglish
Pages (from-to)72-93
Number of pages22
JournalBritish Journal of Mathematical and Statistical Psychology
Issue number1
StatePublished - 1 Feb 2014

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