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

[David Winsemius]

> On Nov 25, 2015, at 8:30 AM, angelo.arcadi at virgilio.it wrote:
> 
> 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?

I suspect that instead of `idesign=~scrd$Subject` that you may want `idesign=~scrd|Subject` or after experimenting with an example in ?Anova, more probably `idesign=~scrd*Subject`

The `$` operator is generally not correctly used in formulas, since it would violate the scoping expectations of the package authors. It would be pulling in a vector of length nrow(scrd) from the object outside the function evaluation frame.

I also question whether the repeated measures within trial might also be needed to be accounted for in the ‘idata' object and ‘idesign' formula. I’m not a real statistician, so this is based more on syntactical reasoning rather than considered statistical advice. You probably do need to be consulting a real statistician.

> 
> Thanks in advance
> 
> Best regards
> 
> Angelo
> 
> 	[[alternative HTML version deleted]]

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> 
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David Winsemius
Alameda, CA, USA