[R] Type III sum of squares and appropriate contrasts

Marc Schwartz marc_schwartz at comcast.net
Thu Oct 11 19:42:32 CEST 2007

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


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

Also, see R FAQ 7.18.


Marc Schwartz

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