Re: [R] Type II and III sum of square in Anova (R, car package)

From: <Bill.Venables_at_csiro.au>
Date: Tue 29 Aug 2006 - 09:36:25 EST


I cannot resist a very brief entry into this old and seemingly immortal issue, but I will be very brief, I promise!

Amasco Miralisus suggests:

> As I understood form R FAQ, there is disagreement among Statisticians
> which SS to use
>
(http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-does-the-output-from-a nova_0028_0029-depend-on-the-order-of-factors-in-the-model_003f).

To let this go is to concede way too much. The 'disagreement' is really over whether this is a sensible question to ask in the first place. One side of the debate suggests that the real question is what hypotheses does it make sense to test and within what outer hypotheses. Settle that question and no issue on "types" of sums of squares arises.

This is often a hard question to get your head around, and the attraction of offering a variety of 'types of sums of squares' holds out the false hope that perhaps you don't need to do so. The bad news is that for good science and good decision making, you do.

Bill Venables.



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