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

Prof Brian Ripley ripley at stats.ox.ac.uk
Mon Oct 22 10:50:10 CEST 2007

```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
>
>
>
> 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
> BELGIUM                      WWW: http://iridia.ulb.ac.be/~mmanfrin
>
> gpg DSA: 0xD3956AAF
> gpg fingerprint: 1D69 8664 EF25 FCDE 229F FCA1 E66F EAC5 D395 6AAF
> --------------------------------------------------------------------
>
>

--
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
```