[R] Degree of freedom for contrast t-tests in lme

From: S Nakagawa <S.Nakagawa_at_sheffield.ac.uk>
Date: Thu 23 Feb 2006 - 09:37:40 EST

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 Nakagawa
Department of Animal & Plant Sciences,
University of Sheffield,	
Sheffield S10 2TN, UK
Tel: +44-114-222-0064  
Fax: +44-114-222-0002

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Received on Thu Feb 23 10:02:21 2006

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