Message-ID: <1140647860.43fce7b42ec27@webmail.shef.ac.uk>
Date: 2006-02-22T22:37:40Z
From: Shinichi Nakagawa
Subject: Degree of freedom for contrast t-tests in lme
Dear all
Somebody may have asked this before but I could not find any answers in the web
so let me ask a question on lme.
When I have a fixed factor of, say, three levels (A, B, C), in which each level
has different size (i.e. no. of observations; e.g. A>B>C). When I run an lme
model, I get the same degree of freedom for all the contrast t-tests (e.g. AvsB
or BvsC). I have tried this to several data sets but the same thing happened.
Whatever sample size I have in different levels (in a fixed factor), I get the
same degree of freedom for t-tests.
Why is this? Is this how mixed-effects model work? Does this mean that if I have
unbalanced design, results from lme are likely to be wrong?
Thank you for your help
Shinichi
--
Shinichi Nakagawa
Department of Animal & Plant Sciences,
University of Sheffield,
Sheffield S10 2TN, UK
Tel: +44-114-222-0064
Fax: +44-114-222-0002