Re: [R] 2^2 problem revisited

From: Rolf Turner <r.turner_at_auckland.ac.nz>
Date: Fri, 14 Nov 2008 11:42:02 +1300

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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> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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