Message-ID: <x2ekj96ajj.fsf@biostat.ku.dk>
Date: 2004-11-04T12:52:48Z
From: Peter Dalgaard
Subject: Specifying error terms in aov and lme
In-Reply-To: <Pine.LNX.4.44.0411041218060.28041-100000@red00.iridis.soton.ac.uk>
Nathaniel Street <N.R.STREET at soton.ac.uk> writes:
> I need to specify error terms properly in a mixed-effects anova model. I
> know you can add error terms in aov using Error and can specify random
> factors in lme but I am not sure how these get treated.
>
> When making the calculations for fixed and random factors, are the correct
> error terms used and how can you get aov or lme to use different error
> terms for fixed and random effects?
In short: Those considerations make sense for programs that give you
only a partitioning of the sum of squares. aov() and lme() should
(mostly) get things right automatically *if* you specify the model
correctly. With aov() you still need some know-how to test
significance of variance components, though.
> I'm basing the need for this on this table from Zar,
>
> Both fixed factors - both tested against error
Now that can actually be horribly wrong if there is significant
interaction.
> Both random factors - both tested against interaction MS
> 1 fixed - interaction MS
> 1 random - replicate MS
wrong again.....
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907