Re: [Rd] aov for unbalanced design (PR#7144)

From: Thomas Lumley <tlumley_at_u.washington.edu>
Date: Fri 30 Jul 2004 - 08:09:01 EST

It is not a bug. It is supposed to be that way. It is even a FAQ.

        -thomas

On Thu, 29 Jul 2004 tlogvinenko@partners.org wrote:

> Full_Name: Tanya Logvinenko
> Version: 1.7.0
> 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
>
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>

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley@u.washington.edu	University of Washington, Seattle

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