IntroductionOne-way repeated measures ANOVA requires sphericity. Research indicates that violation of this assumption has an important impact on Type I error. Although more advanced alternative procedures exist, most classical texts recommend the use of adjustedF-tests, which are frequently employed because they are intuitive, easy to apply, and available in most statistical software. AdjustedF-tests differ in the procedure used to estimate the corrective factorε, the most common being the Greenhouse-Geisser (F-GG) and Huynh-Feldt (F-HF) adjustments. Although numerous studies have analyzed the robustness of these procedures, the results are inconsistent, thus highlighting the need for further research.MethodsThe aim of this simulation study was to analyze the performance of theF-statistic,F-GG, andF-HFin terms of Type I error and power in one-way designs with normal data under a variety of conditions that may be encountered in real research practice. Values ofεwere fixed according to the Greenhouse–Geisser procedure (ε̂). We manipulated the number of repeated measures (3, 4, and 6) and sample size (from 10 to 300), withε̂values ranging from the lower to its upper limit.ResultsOverall, the results showed that theF-statistic becomes more liberal as sphericity violation increases, whereas bothF-HFandF-GGcontrol Type I error; of the two,F-GGis more conservative, especially with large values ofε̂and small samples.DiscussionIf different statistical conclusions follow from application of the two tests, we recommend usingF-GGforε̂values below 0.60, andF-HFforε̂values equal to or above 0.60.
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