[R] Beginner: Homogenity of Variances
Markus.Koesters at uni-jena.de
Sat Nov 1 17:18:40 CET 2003
Thank you very much for the quick answer, I'll try that.
The dependence for the other samples are a result of the designs of
the studies I want to metaanalyse - most of them are single group
studies with pre-post measures.
> I don't see a way to use var.test without data vectors. However,
> you could trick it as illustrated by the following:
> SD1 <- SD2 <- N1 <- N2 <- 5
> var.test(SD1*rnorm(N1), SD2*rnorm(N2))
> For more than two variances, you could use bartlett.test
> similarly. However, Bartlett's test, and presumably also var.test, is
> highly sensitive to non-normality. I don't have a citation, but I
> remember hearing George Box say that Bartlett's test is almost a better
> test of non-normality than of inhomogeneity of variance. If you needed
> a citation for that, I would look first at various papers and book
> sections discussing robustness and Bartlett's test, especially in the
> index of Box on Quality and Discovery (Wiley, 2000) or his earlier
> collected works volumes.
> This may answer to "independent samples" question. However, we
> would need to know more about the nature of the dependence to answer the
> dependent samples question, and a sensible answer to the latter may
> require untenable assumptions.
> hope this helps. spencer graves
> Markus Koesters wrote:
> >for my meta-analysis I try to test if two varainces are equal without
> >using the raw scores. I have is the SD's, N's and the Means.
> >I want to test the variances from dependent and independend
> >I assume I can use the var.test procedure for the independent
> >samples, but what about the dependent samples ? Has anyone an
> >idea how to realise this with R ?
> >Thanks in advance
> >R-help at stat.math.ethz.ch mailing list
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