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

[Max Manfrin]

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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Max MANFRIN                                 Tel.: +32 (0)2 650 3168
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1050 Brussels                             Email: mmanfrin at ulb.ac.be
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