ANOVA, ANCOVA significance

[morphmet]

-------- Original Message --------
Subject:        ANOVA, ANCOVA significance
Date:   Fri, 28 Aug 2009 10:02:29 -0700 (PDT)
From:   Javier Santos <javiersant...@hotmail.com>
To:     <morphmet@morphometrics.org>



Hello all,

I had a question conserning the ANOVA analysis between three groups. In
the overall ANOVA testing for differences between groups (F-statistic) I
get unsignificant differences, while in pairwise t-testing significant
differences between groups do appear for variables with unsignficant
F-statistics. Should the significant t-tests be taken as valid, or only
those which have first been significant under the F-statistic?
I also extend this question to ANCOVA analysis, the only difference here
being that the F-statistic is always used (at least in SPSS). What I
changed is the independent factor used from "species" to a pairwise
factor: "a-b", "a-c", "b-c".  By doing so, I also come across variables
that are unsignificant when using "species", but that are significant in
one of the pairwise tests i.e. "a-b".
Does anyone know how I should interpret these results?

Many thanks,
Javier Santos
javiersant...@hotmail.com <mailto:javiersant...@hotmail.com>
Ugent / USAL

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