[R] contrasts in a type III anova

[David Jutier]

Hello,

I use a type III anova ("car" package) to analyse an unbalanced data design. I 
have two factors and I would have the effect of the interaction. I read that 
the result could be strongly influenced by the contrasts. I am really not an 
expert and I am not sure to understand indeed about what it is...

Consequently, I failed to properly used the fit.contrast function (gregmisc 
package) because I don't understand what the fonction need in the argument 
"coeff".

The two factors are Y (Ya, Yb,..., Ye) and Auto (Auto1, Auto2,...., Auto10)
The responses are binomial (counts in the matrice "mat") and gaussian 
(variable "tot"). I use the glm procedure :

glm1 <- glm (mat ~ y*auto, data, family=binomial)
glm2 <- glm (tot ~ y*auto, data, family=gaussian)

Subsequently I use the Type III anova :

Anova (glm1, type="III")
Anova (glm2, type="III")

Using the contrast.treatment for both factors Y and Auto, R gives coherent 
results, but I really not sure that this contrasts are appropriate !

Thank's for your advices !
David