[R] Syntax error in using Anova (car package)

[angelo.arcadi at virgilio.it]

Dear list members,
I am getting an error while performing a repeated measures MANOVA using the Anova function 
of the "car" package. I want to apply it on the results of an experiment involving 19 participants, 
who were subjected to 36 stimuli, each stimulus was repeated twice for a total of 72 trials 
per subject. Participants had to adjust two parameters of sounds, Centroid and Sound_Level_Peak, 
for each stimulus. This is the head of my dataset (dependent variables: Centroid and 
Sound_Level_Peak; independent variables: Mat (6 levels) and Sh (2 levels)). 

> head(scrd)
    Subject         Mat   Sh      Centroid            Sound_Level_Peak
1     Subject1      C     DS        1960.2               -20.963
2     Subject1      C     SN        5317.2               -42.741
3     Subject1      G     DS       11256.0               -16.480
4     Subject1      G     SN        9560.3               -19.682
5     Subject1      M     DS        4414.1               -33.723
6     Subject1      M     SN        4946.1               -23.648


Based on my understanding of the online material I found, this is the procedure I used:

idata <- data.frame(scrd$Subject)
mod.ok <- lm(cbind(Centroid,Sound_Level_Peak) ~  Mat*Sh,data=scrd)
av.ok <- Anova(mod.ok, idata=idata, idesign=~scrd$Subject)


I get the following error

Error in check.imatrix(X.design) : 
  Terms in the intra-subject model matrix are not orthogonal.


Can anyone please tell me what is wrong in my formulas?

Thanks in advance

Best regards

Angelo





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