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

[Thomas Lumley]

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

	-thomas

On Thu, 29 Jul 2004 tlogvinenko at 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 at u.washington.edu	University of Washington, Seattle