I have data of 6 groups with sample size of n = 2, 10, 2, 9, 3, 1 and I want to perform Permutational multivariate analysis of variance (PERMANOVA) on these data.
My question is: Is it correct to run perMANOVA on these data with the small sample size? The results look strange for me because the group of n = 1 showed insignificant difference to other groups although the graphical representation of the groups clearly show a difference.
Thank you
MANOVA emphasizes the attributescattering in the study group and the logic of this analysis is based on the scattering of scores. It is not recommended to use small groups with one or more people (I mean less than 20 people) to perform parametric tests such as MANOVA. In my opinion, use non-parametric tests to examine small groups.
I personally wouldn't do that. I would suggest that you increase your sample sizes. BTW your sample with n=1 has infinite variance which is why you observe that result. Best wishes David Booth
Hello Rahma,
I agree with the two posts above; your sample size is simply too small to yield a stable solution via manova. Note that the n = 1 cell contributes a constant value for that cell's mean, no matter what you do by way of permutations.
Finally, note that the effective per-cell sample size with unequal cell n for one-way designs tracks well to the harmonic mean of n. For your data set as it stands, that means an "effective" per-cell n of about 2.4. Unless differences are gigantic on the DV set, no procedure (parametric or exact/permutation) will have the statistical power to detect differences with that size.
Good luck with your work.
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