[R] Dominant factors in aov?

[Jonathan Baron]

I'm not a statistician, so take what I say with a grain of salt.

On 12/02/04 06:29, Rene Eschen wrote:
>Can someone explain me why factor C has only 25 Df (in stead of 28, what I
>expected), and why this number changes when I leave out factors B or C (but
>not A)? Why do factors B and C (but again: not A) not show up in the
>calculation if they appear later in the formula than D?
>
>When I ask summary.lm(aov(Y~A+B+C+D+E)), R tells me that three levels of D
>were not defined because of "singularities" (what does this word mean?).
>After checking and playing around with the dataset, I find no logical reason
>for which levels are not defined. Even if I construct a "perfect" dataset
>(balanced, no missing values) I never get the correct number of Df.

I would guess that the factors are somewhat predictable from each
other.  That is, there is some redundancy.  Try predicting each
factor from all the others, without the dependent variable.

Jon
-- 
Jonathan Baron, Professor of Psychology, University of Pennsylvania
Home page: http://www.sas.upenn.edu/~baron
R search page: http://finzi.psych.upenn.edu/