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    Question about permutations ANOVA test




    Hello everyone,
    I have data of a variable from 4 sites, with 3 repetitions from each site. Tests revealed that I do have homoscedasticity but no normality. So I chose to use a test of permutations to ANOVA. A few days ago someone told me that I cannot do this test if I have 4 sites and only 3 repetitions. My questions are:

    1. Is this true? and if so:

    2. What other test should I choose?


    Thank you very much,
    Roy.

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    Re: Question about permutations ANOVA test

    I wonder if you can use the typical approach, but with robust standard error estimates?
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    Re: Question about permutations ANOVA test

    How did you test for normality? Was it on the raw response?
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    Re: Question about permutations ANOVA test

    Quote Originally Posted by hlsmith View Post
    I wonder if you can use the typical approach, but with robust standard error estimates?

    I'm not sure I understand. Can you elaborate?

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    Re: Question about permutations ANOVA test

    Quote Originally Posted by Dason View Post
    How did you test for normality? Was it on the raw response?

    I used the Shapiro-Wilk test. I don't know if I should put any efforts in trying to pass it as normal distributed since it has only 3 repetitions.

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    Re: Question about permutations ANOVA test

    Right. I was asking if you just did the test on the raw responses or were you looking at the residuals from the anova?
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    Re: Question about permutations ANOVA test

    Maybe this link can help. Here the number of replicates is also three, but with 24 observation and an extra factor. So I guess that your study is OK.

    The test says:
    "The data do not have to be normal (and these data certainly are not) or have any other specific distribution. But notice that requiring the errors of observations to be iid brings in the traditional assumption of homogeneity of variance."

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    Re: Question about permutations ANOVA test

    Quote Originally Posted by Dason View Post
    Right. I was asking if you just did the test on the raw responses or were you looking at the residuals from the anova?

    Oh, sorry. On the raw responses.

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    Re: Question about permutations ANOVA test


    Quote Originally Posted by GretaGarbo View Post
    Maybe this link can help. Here the number of replicates is also three, but with 24 observation and an extra factor. So I guess that your study is OK.

    The test says:

    Yes, that does look a lot like my data (in structure). Maybe it is the right test. Although there is no specific discussion regarding the amount of repetitions.

    Thank you very much!

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