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Re: st: My ANOVA and regression results don't agree


From   Phil Schumm <[email protected]>
To   Statalist Statalist <[email protected]>
Subject   Re: st: My ANOVA and regression results don't agree
Date   Tue, 7 Jan 2014 05:54:36 -0600

On Jan 6, 2014, at 8:59 PM, David Hoaglin <[email protected]> wrote:
> Doesn't the ANOVA of those systolic data have some features of regression, because of the imbalance (18 observations in 4 cells)?  In the Partial SS column, sum of the SS for drug, disease, and drug#disease is less than the SS for the model.


David,

I'm not sure I understand your question (sorry).  It's true that the example I gave was unbalanced, and that therefore the main effects are not orthogonal; moreover, interpreting them requires care.  That said, I interpreted the original question as having to do with the difference between so-called dummy variable coding and the deviations from the (balanced) grand mean.  The question of how to interpret the latter in the unbalanced case and/or in the presence of interaction is a separate issue, though certainly important.  Perhaps I should have commented on this too.

If you see another issue that I am missing here, please let me know.

Thanks,


-- Phil


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