# Non-normal Data in Repeated Measures ANOVA: Impact on Type I Error and Power

“Non-normal Data in Repeated Measures ANOVA: Impact on Type I Error and Power” (2023), by María J. Blanca et al. Mathematics research paper. Original abstract below, unchanged. No free PDF was found.

- Authors: María J. Blanca, Jaume Arnau, F. Javier García-Castro, Rafael Alarcón, Roser Bono
- Published: February 1, 2023
- Field: Mathematics
- DOI: https://doi.org/10.7334/psicothema2022.292
- Source: https://doi.org/10.7334/psicothema2022.292

## Abstract

BACKGROUND: Repeated measures designs are commonly used in health and social sciences research. Although there are other, more advanced, statistical analyses, the F-statistic of repeated measures analysis of variance (RM-ANOVA) remains the most widely used procedure for analyzing differences in means. The impact of the violation of normality has been extensively studied for between-subjects ANOVA, but this is not the case for RM-ANOVA. Therefore, studies that extensively and systematically analyze the robustness of RM-ANOVA under the violation of normality are needed. This paper reports the results of two simulation studies aimed at analyzing the Type I error and power of RM-ANOVA when the normality assumption is violated but sphericity is fulfilled. METHOD: Study 1 considered 20 distributions, both known and unknown, and we manipulated the number of repeated measures (3, 4, 6, and 8) and sample size (from 10 to 300). Study 2 involved unequal distributions in each repeated measure. The distributions analyzed represent slight, moderate, and severe deviation from normality. RESULTS: Overall, the results show that the Type I error and power of the F-statistic are not altered by the violation of normality. CONCLUSIONS: RM-ANOVA is generally robust to non-normality when the sphericity assumption is met.

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