[R] Function to separate effect in AOV
Ronaldo Reis Junior
chrysopa at gmail.com
Tue Jul 24 00:04:55 CEST 2007
Hi,
I have a dummy question.
Suppose that I have two explanatory variable, T1 (A, B) and T2 (C, D) and one
response variable.
> attach(dados)
> tapply(Y,list(T1,T2),mean)
C D
A 2.200000 10.20000
B 2.223333 20.26667
In this case, "A" and "B" inside "C" have no difference, but have differences
inside "D"
I make this model:
> m <- aov(Y~T1*T2)
>
> summary(m)
Df Sum Sq Mean Sq F value Pr(>F)
T1 1 76.36 76.36 5617.9 1.119e-12 ***
T2 1 508.69 508.69 37426.7 5.704e-16 ***
T1:T2 1 75.65 75.65 5566.0 1.161e-12 ***
Residuals 8 0.11 0.01
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
This result don't show the reality of the data, because I cant see that "A"
and "B" inside "C" are the same.
The anova result is the same of an full different levels, like this:
> attach(dados2)
>
> tapply(Y,list(T1,T2),mean)
C D
A 6.100000 10.20000
B 2.223333 20.26667
>
> m <- aov(Y~T1*T2)
>
> summary(m)
Df Sum Sq Mean Sq F value Pr(>F)
T1 1 28.74 28.74 2114.3 5.529e-11 ***
T2 1 367.75 367.75 27056.7 2.088e-15 ***
T1:T2 1 145.81 145.81 10728.1 8.433e-14 ***
Residuals 8 0.11 0.01
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
In this case all level are different, C to D and A to B.
The question is:
The only way to find this real difference is:
1) make T1 and T2 like a Treatment variable with 4 levels (AC,BC,AD,BD)?
or
2) make 3 anova:
a) Anova (A,B) inside C
b) Anova (A,B) inside D
c) Full factorial Anova (like this in the e-mail)
or
3) exist any other way to make this in only one analysis, to find all
differences e interactions? In other words, to find differences in "A"
and "B" inside "C", "A" and "B" inside "D", "C" and "D" inside "A" and "C"
and "D" inside "B"
Thanks
Ronaldo
--
> Prof. Ronaldo Reis Júnior
| .''`. UNIMONTES/Depto. Biologia Geral/Lab. de Ecologia
| : :' : Campus Universitário Prof. Darcy Ribeiro, Vila Mauricéia
| `. `'` CP: 126, CEP: 39401-089, Montes Claros - MG - Brasil
| `- Fone: (38) 3229-8187 | ronaldo.reis em unimontes.br | chrysopa em gmail.com
| http://www.ppgcb.unimontes.br/ | ICQ#: 5692561 | LinuxUser#: 205366
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