[Rd] aov for unbalanced design (PR#7144)
Prof Brian Ripley
ripley at stats.ox.ac.uk
Fri Jul 30 07:07:22 CEST 2004
What do you think is the correct answer and on what authority?
(These are explicitly sequential aka Type 1 anova tables.)
That the SSqs depend on the order of fitting is a feature of an unbalanced
design. I believe that R is correct and your understanding is not.
On Thu, 29 Jul 2004 tlogvinenko at partners.org wrote:
> Full_Name: Tanya Logvinenko
> Version: 1.7.0
Oh, please! Don't send in bug reports from very old versions -- there
have been 5 releases since then.
> OS: Windows 2000
> Submission from: (NULL) (132.183.156.125)
>
>
> For unbalanced design, I ran into problem with ANOVA (aov function). The sum of
> squares for only for the second factor and total are computed correctly, but sum
> of squares for the first factor is computed incorreclty. Changing order of
> factors in the formula changes the ANOVA table. For the balanced design, there
> is no such problem.
>
> > summary(aov(data[1,]~factor1+factor2))
> Df Sum Sq Mean Sq F value Pr(>F)
> factor1 5 1524420 304884 6.4529 0.0003229 ***
> factor2 7 1447830 206833 4.3776 0.0017808 **
> Residuals 31 1464674 47248
> ---
> Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
> > summary(aov(data[1,]~factor2+factor1))
> Df Sum Sq Mean Sq F value Pr(>F)
> factor2 7 1648225 235461 4.9836 0.0007295 ***
> factor1 5 1324025 264805 5.6046 0.0008612 ***
> Residuals 31 1464674 47248
> ---
> Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
The FAQ has a section on BUGS asking for a *reproducible* example. This
is not.
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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