Hello,
If you are only interested in the group difference then demeaning makes no difference here. Also as the group regressors contain the global mean, there is no need to use the -D option in either case.
Kind Regards
Matthew
--------------------------------
Dr Matthew Webster
FMRIB Centre
John Radcliffe Hospital
University of Oxford
> On 4 Oct 2017, at 07:56, Manuel Blesa <[log in to unmask]> wrote:
>
> Hi all,
>
> I have a similar doubt, I've been reading about when to demean or not and when to use the -D option. But I'm a little bit confused.
>
> In my case I want to compare two different groups, adjusting for some covariates (some of them are binary), the design matrix looks something like that:
>
> 1 0 284 0 1
> 1 0 296 1 1
> .....
> 0 1 290 1 0
> 0 1 293 0 0
>
> Should I use this or should I demean my covariates?
>
> 1 0 -9 -0.7 0.4
> 1 0 1 0.3 0.4
> ...
> 0 1 -5 0.3 -0.6
> 0 1 -2 -0.7 -0.6
>
> From what I read, I think that in this specific case there is no difference to use one of the other, but demeaning is harmless. Am I correct or should I use the demeaned version? I also have to use the -D in the randomise command? Thanks in advance?
>
> Regards,
>
> Manuel
> ...
