[R] 2^2 problem revisited

[Rolf Turner]

Please read and understand the response that I already sent you
on this issue.

	Rolf Turner

On 14/11/2008, at 10:44 AM, Edna Bell wrote:

> Dear R gurus:
>
> Here is the following from Montgomery's Design and Analysis of
> Experiments, 5th edition.
>
>> str(rout1.df)
> 'data.frame':   16 obs. of  3 variables:
>  $ resp: num  18.2 18.9 12.9 14.4 27.2 24 22.4 22.5 15.9 14.5 ...
>  $ A   : Factor w/ 2 levels "-1","1": 1 1 1 1 2 2 2 2 1 1 ...
>  $ B   : Factor w/ 2 levels "-1","1": 1 1 1 1 1 1 1 1 2 2 ...
>> rout1.df
>    resp  A  B
> 1  18.2 -1 -1
> 2  18.9 -1 -1
> 3  12.9 -1 -1
> 4  14.4 -1 -1
> 5  27.2  1 -1
> 6  24.0  1 -1
> 7  22.4  1 -1
> 8  22.5  1 -1
> 9  15.9 -1  1
> 10 14.5 -1  1
> 11 15.1 -1  1
> 12 14.2 -1  1
> 13 41.0  1  1
> 14 43.9  1  1
> 15 36.3  1  1
> 16 39.9  1  1
>> rout1.aov <- aov(resp~A*B,data=rout1.df)
>> summary(rout1.aov)
>             Df  Sum Sq Mean Sq F value    Pr(>F)
> A            1 1107.23 1107.23 185.252 1.175e-08 ***
> B            1  227.26  227.26  38.023 4.826e-05 ***
> A:B          1  303.63  303.63  50.801 1.201e-05 ***
> Residuals   12   71.72    5.98
> ---
> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
>>
>
> When you test on interaction, you reject (of course).
>
> Now, I thought that you could not test on the main effects, A and B.
> Is that true, please?
>
> Thanks,
> Edna Bell
>
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