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I have 3 groups of 30 fish.

group 1: without anaesthesia
group 2: clove oil anaesthesia
group 3: MS-222 anaesthesia

Every group was investigated at six levels of time (0, 0.5, 1, 2, 6 and 24 hours after anaesthesia). The data aren't normal. Which test to use? Kruskal-Wallis or Friedman?

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    $\begingroup$ What is your exact research question? Do you want to check all 6 levels of time or only the final level with respect to initial level? What exactly are you testing? Is the outcome variable a numeric one or categorical / ordered? Add more details to your question. $\endgroup$ – rnso Apr 12 '15 at 7:32
  • $\begingroup$ I want to compare all 6 levels of time in within and between groups. In fact, I want to compare the effects of different methods of anesthesia on the number of the specific cells. $\endgroup$ – Sara Apr 13 '15 at 13:20
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    $\begingroup$ Graphical methods may be the best for this. If you post some sample data here, it will be helpful. $\endgroup$ – rnso Apr 13 '15 at 14:44
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Briefly spoken you use the Kruskal-Wallis test if the data has unmatched pairs and the Friedman-test is the data has matched pairs.

In my opinion the data of the three tests is unmatched. Therefore the Kruskal-Wallis test is the better test.

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