Listers,
I am running a TBSS analysis using randomise. I have set up my design matrix
and demeaned my single covariate. From reading the list, I am a bit confused
about modeling the mean, I believe I have done so with EV1 EV2 and EV3, and
hence do not need -D. I have an uneven numbers of subjects in my groups, but
all other values are 0s, so I think this successfully models the mean, correct?
My other question is about creating the null distribution. I want to test
the differences between three groups of probands, with fairly limited
subjects in each group: 11,12,14. So comparing each group that leaves me
with 6 contrasts, 7 if I include my covariate. I also will run an F-Test on
two of the independent contrasts (all three groups included). Finally to my
question, can including extra control subjects in my design matrix say EV4
or EV4+EV5 help create a more accurate null distribution, even if I end up
not testing against these EVs at all in my contrast file? Thanks for any help.
EV1 EV2 EV3 EV4
0 1 0 (demeaned covariate)
1 0 0
0 1 0
0 0 1
0 0 1
0 0 1
|