[R-sig-ME] (SMALL CORRECTION): Tukey after lme does not match

[Andrew Robinson]

Dear Alen,

I suggest that it might be useful for you to do some background
reading on the purposes and interpretations of Wald tests (which are
the tests that you are interpreting directly from lme) and
Tukey-corrected tests (from the Tukey output).

But, very briefly, it would be very surprising if the two were to
agree.  The Wald tests p-values are computed for each test as though
it were the only one under consideration, whereas the Tukey p-values
are computed taking account of the inference of the other tests.  So,
the more comparisons being performed at the same time (here, 6 + 5 + 4
+ 3 + 2 + 1 = 21), the more conservative Tukey will be, whereas the
Wald test will not change.

I hope that this helps --- but I reiterate my recommendation for
background reading.

Andrew

On Fri, Jan 6, 2012 at 11:28 AM, Alen Hajnal <Alen.Hajnal at usm.edu> wrote:
> Actually 0vs75 is also significant according to Tukey, but there is still no perfect match with the initial lme analysis.
>
>
> ----------
> Alen Hajnal, PhD.
> Department of Psychology
> The University of Southern Mississippi
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-- 
Andrew Robinson
Deputy Director, ACERA
Senior Lecturer in Applied Statistics                      Tel: +61-3-8344-6410
Department of Mathematics and Statistics            Fax: +61-3-8344 4599
University of Melbourne, VIC 3010 Australia
Email: a.robinson at ms.unimelb.edu.au    Website: http://www.ms.unimelb.edu.au

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