Anova Assumptions Sample Size. Jan 02 2009 What is the sample size needed for the ANOVAs in my dissertation or thesis. Like all parametric tests assumptions are made about the data in order to justify and trust estimates and inferences drawn from ANOVA.
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Thus I can say that I have unequal sample sizes for Mixed ANOVA. The sample size calculation is based a lot of assumptions. Its probably not a coincidence that the biggest group is the only one flagged as being nonnormal.
This is especially the case with large samples as power of the test increases with the sample size.
The estimated probability is a function of sample size variability level of significance and the difference between the null and alternative hypotheses. When I do the analysis by using SPSS it calculates the sum of squares and degrees of freedom by using the minimum sample size of the first group which is 490. Has the same goal than the ANOVAcompare 3 or more groupsbut it uses sample medians instead of sample means to compare groups. The sample size calculation is based a lot of assumptions.
