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Thread: ANOVA with unequal sample sizes

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    ANOVA with unequal sample sizes




    hello,

    I have a question about ANOVA. This is the output I received when testing the effect of 'opnop' on mmse1.
    opnop is divided in 4 groups, but one group had a sample size of 4, while the other groups are bigger. What can the problem be when you decide to continue your exercise with such a difference??

    OPNOP mean group size SD variance
    1 19,00 4 6,583 43,33
    2 20,00 22 9,217 84,95
    3 19,50 20 7,178 51,53
    4 16,00 13 8,727 76,17
    Totaal 18,88 59 8,253 68,11

    I really hope someone can help with this because I can't find the answer ...

    Thanks!

  2. #2
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    With such low number of cases, you would have a high chance of type II error. Furthermore, ANOVA is sensitive to sample size. Instead, in this case, you can run nonparametric Kruskal-Wallis test followed by Mann-Whitney U test for each pair.

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