[R] MANCOVA

[Jonathan DuBois]

Hi,

I have been using R to do multiple analyses of variance with two
covariates, but recently found that the results in SPSS were very
different. I have check several books and web resources and I think
that both methods are correct, but I am less familiar with R, so I was
hoping someone could offer some suggestions. Oddly simple ANOVA is the
same in SPSS and R. Including covariates improves the main effect
(p-value) in R and diminishes it in SPSS..

The formula I have been using is:
>Y = cbind(dV1, dV2, dV3)
>aov(lm(Y~iV1+cV1+cV2))

The main independent variable is disease group and the covariates are
continuous nuisance variables such as age. Both nuisance variables
interact with the dependent variable but not each other. The frequency
distribution of the covariates is similar for each group, but the
groups are not matched 1 to 1. Therefore we would like to control for
these factors statistically. Is this the proper formula for such a
test? If so, what might be cause of major discrepancy with SPSS?

Thanks ahead of time

Best,
Jon