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