[R] "Estimate effects may be unbalanced" in aov()

[Prof Brian Ripley]

On Mon, 22 Oct 2007, Max Manfrin wrote:

> Can anybody explain me what does it mean "Estimated effects may be 
> unbalanced", and what does it imply for the anova analysis?

The help page does!  I suspect you intended to use factors, and have not 
done so, and also that you did not intend to replicate res.

Try

D <- expand.grid(A=factor(c(0,1,2,3)),B=factor(c(0,1)),C=factor(c(0,1)))
aov(rnorm(16) ~ A * B * C, data = D)

>
> Here a case example of what I get.
>
>> D<-expand.grid(A=c(0,1,2,3),B=c(0,1),C=c(0,1),res=c(runif(30,0,1)))
>> aov(res~A*B*C,data=D)
> Call:
>  aov(formula = res ~ A * B * C, data = D)
>
> Terms:
>                      A        B        C      A:B      A:C      B:C    A:B:C 
> Residuals
> Sum of Squares   0.00000  0.00000  0.00000  0.00000  0.00000  0.00000 
> 0.00000  50.93402
> Deg. of Freedom        1        1        1        1        1        1 
> 1       472
>
> Residual standard error: 0.3284982
> Estimated effects may be unbalanced
>
> Thanks in advance
>
>
> PS: > R.Version()
> $platform
> [1] "powerpc-apple-darwin8.10.1"
>
> $arch
> [1] "powerpc"
>
> $os
> [1] "darwin8.10.1"
>
> $system
> [1] "powerpc, darwin8.10.1"
>
> $status
> [1] ""
>
> $major
> [1] "2"
>
> $minor
> [1] "6.0"
>
> $year
> [1] "2007"
>
> $month
> [1] "10"
>
> $day
> [1] "03"
>
> $`svn rev`
> [1] "43063"
>
> $language
> [1] "R"
>
> $version.string
> [1] "R version 2.6.0 (2007-10-03)"
>
>
> --------------------------------------------------------------------
> Max MANFRIN                                 Tel.: +32 (0)2 650 3168
> IRIDIA - CoDE, CP 194/6                     Fax.: +32 (0)2 650 2715
> Université Libre de Bruxelles
> Av. F. D. Roosevelt, 50
> 1050 Brussels                             Email: mmanfrin at ulb.ac.be
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>
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> --------------------------------------------------------------------
>
>

-- 
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