[R] Anova problem with order of terms in model
Martin Julien
martin.julien.2 at courrier.uqam.ca
Tue Jan 17 21:33:57 CET 2006
Hi
I have a linear model and I want to tests whether the model terms are
significant
I used anova but F and P value depend on the order of the terms in the
model.
I have repeated the same analysis in another stat software and F and P value
did not differ with order of terms in the model.
Can anyone can explain what happen or what am I doing wrong ?
In R
> anova (lm(Y~X.1+X.2))
Analysis of Variance Table
Response: Y
Df Sum Sq Mean Sq F value Pr(>F)
X.1 1 4.0351 4.0351 6.5187
0.01852
X.2 1 0.5903 0.5903 0.9537
0.33991
Residuals 21 12.9991 0.619
> anova (lm(Y~X.2+X.1))
Analysis of Variance Table
Response: Y
Df Sum Sq Mean Sq F value Pr(>F)
X.2 1 1.9651 1.9651 3.1747
0.08926
X.1 1 2.6603 2.6603 4.2977
0.05066
Residuals 21 12.9991 0.619
With another stat software (JMP)
Y~X.1+X.2
Df Sum Sq Mean Sq F value Pr(>F)
X.1 1 2.6603 2.6603 4.2977
0.05066
X.2 1 0.5903 0.5903 0.9537
0.33991
Residuals 21 12.9991 0.619
Y~X.2+X.1
Df Sum Sq Mean Sq F value Pr(>F)
X.2 1 0.5903 0.5903 0.9537
0.33991
X.1 1 2.6603 2.6603 4.2977
0.05066
Residuals 21 12.9991 0.619
---------------------------------------------------------------------------
Julien Martin
Canadian Research Chair in behavioural ecology
Université du Québec à Montréal
Email: martin.julien.2 at courrier.uqam.ca
More information about the R-help
mailing list