[R] manova with Error?

RenE J.V. Bertin rjvbertin at hotmail.com
Thu Oct 17 13:25:32 CEST 2002

Let's say I have a within-subject experiment with 2 observables, obs1 and ob2 and 2 independent factors, fac1 and fac2.

I can do

summary( aov( obs1~fac1*fac2 + Error(Subject/(fac1*fac2)) ) )
summary( aov( obs2~fac1*fac2 + Error(Subject/(fac1*fac2)) ) )

to test the 2 observables separately.

> summary( fit<-manova( cbind(obs1,obs2)~fac1*fac2 + Error(Subject/(fac1*fac2)) ) )

gives results that seem sensible, but that I suppose represent the effects on obs1 and obs2 combined. The example for summary.manova shows that 
> summary.aov(fit)
would print the effects separately for each observable. However, I get the message

Error in 1:object$rank : NA/NaN argument

> class(fit)
[1] "aovlist" "listof"

I suppose that this means that I shouldn't want to do this sort of test, and rather look at each observable separately. The question is: why? Is there a simple explanation comprehensible for the non-statistician?

RenE Bertin.
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