[R] type III Sum Sq in ANOVA table - Howto?

Thomas Lumley tlumley at u.washington.edu
Fri Mar 7 16:35:46 CET 2003

On 7 Mar 2003, Peter Dalgaard BSA wrote:
> Hmm... no ... and yes. There are some useful models, but you cannot
> specify them unambiguously with model formulas. At least to my way of
> thinking, the only useful way of thinking of interaction terms is that
> f1:f2 describes an arbitrary pattern of means in the f1 x f2
> crosstable, and the rest is just R/S being helpful in removing known
> aliased effects. So f1 + f2 + f1:f2 is the same model as f2 + f1:f2 is
> the same as f1:f2.

The reason I didn't expect this that it makes : and * synonyms (for
factors).  I realise that the effects are parametrisation-dependent, but
most of the useful output of the model is parametrisation-dependent

OTOH if it's in the White Book, as John Fox indicated, then it's by
definition not a bug.


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