On Jun 12, 2011, at 12:50 , eldor ado wrote:
> dear r community...
>
> it loks like i won't be able to reach homogenity of variance for my
> dataset, so i end up with welch anova instead of regular anova.
> documentation on this test is rather scarce, so maybe someone here can
> enlighten me a bit:
>
> - do i understand that no two-way implementation of the welch anova
> has been developed yet?
Has the THEORY been developed? For complete data, I suppose you can formulate it
as a multivariate contrast test and employ Huynh-Feldt correction, but it is not
quite the obvious generalization. Otherwise, formulate as a mixed model with
error variance depending on treatment, but the degree-of-freedom adjustments are
not implemented in lme.
> - is there a post-hoc test for welch anovas implemented in R?
Again, what does it mean?
pairwise.t.test(..., pool.sd = FALSE, var.eq = FALSE)
will do various pairwise comparison and allow simple corrections of the p value
(Bonferroni and close relatives).
>
> thanks a lot,
> lukas kohl
>
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--
Peter Dalgaard
Center for Statistics, Copenhagen Business School
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