Dear SPMers,
I sent a mail last week and as I received a spam and no answer so I send my questions again.
I'm trying to run a full factorial design with one factor (factor group, 3 groups so 3 levels). Each cell I have entered corresponds to a group. Then I have 3 covariates. One of them is not the same across group. The idea is to show that group differences are not due to these covariates.
Here are my questions:
1) Is this design correct ? Is that ok to say that by adding a covariate in a full factorial design we assume that the effect of the covariate is the same in all groups ?
2) When I run my design, everything is ok til the 11th suject in each group.
(so I have a unique factor). When I run the batch with
11 subjects per group, it's seems to be ok. When I add a 12th subject in
each group, I'm out of memory (with two different PC), although it's not the case in a flexible
design. Is it normal ? Is it very memory-consuming ? Or is my design wrong ?
3) I understand that a full factorial is a fixed-effect analysis, as there is no subject factor. What is annoying for me is that I would like to take into account the between-subject variability, what is possible with a flex. However I can't add a covariate in a flex. So what would be the best model ?
I would be very grateful if someone could help me.
Delphine