Repeated measures analysis on nonparametric data

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Repeated measures analysis on nonparametric data

I have nonparametric data as such for two treatment groups:

ID Group Visit Number Potassium
1 1 01 23
1 1 02 0
1 1 03 100
2 2 01 5
2 2 02 355
2 2 03 100
........and so on.

I would like to compare the means of potassium for the two treatment groups, taking into account the multiple visits (this is where the repeated measures comes in). How do I do this in SAS? Mixed and GLM assume normality and my data are not normal. What kind of test can I use? Please provide examples.

Thank you very much!
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Re: Repeated measures analysis on nonparametric data

If you really want to compare means, you are in the world of parametric statistics. Most of the non-parametric tests examine medians or other characteristics of the distribution.

Friedman's 2-way analysis of variance can handle some types of repeated measures without assuming normality. I'm not sure whether or where it is in SAS.

If you have enough data, you could convert the outcomes to ranks and rely on the central limit theorem to support conclusions based on a parametric analysis.

You might also be able to use a variance stabilizing transformation and apply the parametric methods.
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