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    ANOVA - Greenhouse Geisser




    Hey folks,

    I'm just a little bit confused and hope someone might can help me:

    I'm working on the statistics part of my thesis and performed some ANOVAs with Greenhouse Geisser as correction. Now the thing that suprises me is that SPSS gives me decimal numbers as degrees of freedom for the F value.
    I.e. F(1.461 / 29.227)=....
    In papers I've never seen decimal numbers as df's for F values. They're always whole numbers.. So am I doing sth wrong or is it just normal to round the values?

    Would be glad for some help...

    THX!

    vier.gewinnt

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    Quote Originally Posted by vier.gewinnt View Post

    So am I doing sth wrong or is it just normal to round the values?

    No, you're not doing any wrong. It's just an adjustment to the degrees of freedom when the underlying assumption of homogeneity associated with the covariance matrix is violated....e.g. for a One-Way Within Subjects Design (or Repeated Measures) you would have df(num) = epsilon*(a - 1) and df(den) = epsilon*(n - 1)(a - 1) and where the computation of epsilon is rather complicated.

    Because epsilon is bounded between 1/(a - 1) and 1.0, it will create the decimals your observing.

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    Thank you dragan! So would you rather round the decimals and use whole numbers or keep the decimals for a publication? Do you know wheater there is a convention?

    Thx man...

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    Quote Originally Posted by vier.gewinnt View Post
    Thank you dragan! So would you rather round the decimals and use whole numbers or keep the decimals for a publication? Do you know wheater there is a convention?

    Thx man...

    If it were me, I would just report the usual degrees of freedom and just note that the reported p-value(s) associated with the F statistic(s) are adjusted via Greenhouse-Geisser.

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