[R] A concrete type I/III Sum of square problem

[Prof Brian Ripley]

More to the point, you are confusing multistratum AOV with single-stratuam 
AOV.  For a good tutorial, see MASS4 (bibliographic information in the R 
FAQ).  For unbalanced data we suggest you use lme() instead.

On Tue, 14 Feb 2006, WPhantom wrote:

> Hi R-help members,
>
> I have read a lot in the Archive about the "Type I" vs "Type III" sum
> of square. I think I have read confusing post so
> I want to have a clear idea of the problem.
>
> Here is an example.
> I have 3 groups of subjects of unequal sample size (G1 (n=7), G2
> (n=7), G3 (n=4)).
> for Each subject I have 4 measures corresponding to  the crossing of
> 2 factor  (A & B) of two levels each.
>
> my dependant variable is X.
>
> After reading a lot of tutorials on R I have tried the
> summary(aov(X~GROUP*A*B+Error(SUJECT/(A*B) )
>
> This results are with "type I SS".
>
> What's wrong with these results ? Should I use type III SS and, if so
> how to enter my design in Anova (car package, I still have not the
> J.  Fox's book) ?
> I have clearly not understood the difference between type I & III
> (with the limits of each approach).  A link to a good tutorial on
> this topic will help me a lot.
>
>
>
> Sylvain CLEMENT
> "Neuropsychology & Auditory Cognition Team"
> Lille, FRANCE

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595