[R] "Estimate effects may be unbalanced" in aov()
Max Manfrin
mmanfrin at ulb.ac.be
Mon Oct 22 11:36:44 CEST 2007
On 22 Oct 2007, at 10:50, Prof Brian Ripley wrote:
> 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)
> D<-expand.grid(A=factor(c(0,1,2,3)),B=factor(c(0,1)),C=factor(c
(0,1)))
> D
A B C
1 0 0 0
2 1 0 0
3 2 0 0
4 3 0 0
5 0 1 0
6 1 1 0
7 2 1 0
8 3 1 0
9 0 0 1
10 1 0 1
11 2 0 1
12 3 0 1
13 0 1 1
14 1 1 1
15 2 1 1
16 3 1 1
> aov(rnorm(16) ~ A*B*C, data=D)
Call:
aov(formula = rnorm(16) ~ A * B * C, data = D)
Terms:
A B C A:B A:C
B:C A:B:C
Sum of Squares 9.327827 0.256657 0.172870 4.054674 0.079648 3.214687
2.828070
Deg. of Freedom 3 1 1 3 3
1 3
Estimated effects may be unbalanced
> !is.list(replications(formula=rnorm(16)~A*B*C,data=D))
[1] TRUE
The number of replicates for each factor is the same. I guess that
the unbalanced refers to the number of observations that each level
in a factor has, am I correct?
For calculating HSDTukey confidence intervals for interaction plots
in such unbalanced design, what should I do?
Thanks in advance.
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Université Libre de Bruxelles
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