[R] Type III sum of squares and appropriate contrasts

[Marc Schwartz]

On Thu, 2007-10-11 at 10:24 -0700, Menelaos Stavrinides wrote:
> I am running a two-way anova with Type III sums of squares and would
> like to be able to understand what the different SS mean when I use
> different contrasts, e.g. treatment contrasts vs helmert contrasts. I
> have read John Fox's "An R and S-Plus Companion to Applied Regression"
> approach -p. 140- suggesting that treatment contrasts do not usually
> result in meaningful results with Type III SS but it's not clear to me
> why. Any suggestions on a stats text discussing this would be greatly
> appreciated.
> Thanks,
> Mel


A good place to start would be Prof. Venables' "Exegeses on Linear
Models":

  www.stats.ox.ac.uk/pub/MASS3/Exegeses.pdf 

Searching the r-help archives will also yield many discussions.

Also, see R FAQ 7.18.

HTH,

Marc Schwartz