Hi,
If you do a difference between two EVs in your contrast then it
doesn't matter.
It is like doing (effect1 - baseline) - (effect2 - baseline) =
(effect1 - effect2)
Note that this is true for any contrast that adds up to zero.
So in contrasts like that the baseline is irrelevant.
But in the simple "1 0 0 ..." type of contrasts it obviously is
important and you are
looking at effect1 wrt baseline.
All the best,
Mark
On 15 Feb 2008, at 18:23, carlos silva pereira wrote:
> Thanks for the quick reply!
> One last thing: when I specify a contrast between two EVs, will
> they be previously contrasted to the baseline to?
> For example: in contrast1 I define a value of 1 for EV1 and in
> contrast2 I define 1 for EV1 and -1 for EV2.
> In contrast2 will EV1 and EV2 be contrasted to baseline also or
> just to each other?
> Thanks again, this forum is a major help for starters!
> Carlos
>
> On 15/02/2008, Mark Jenkinson <[log in to unmask]> wrote: Hi,
>
> You should not use baseline EVs in Feat.
> It may work, but it will be close to rank deficient normally.
> The best way is to omit it and then all EVs are implicitly contrasted
> wrt baseline and the modeling inside Feat works optimally.
>
> All the best,
> Mark
>
>
>
> On 15 Feb 2008, at 18:10, carlos silva pereira wrote:
>
> > Hi to all!
> > Basic question: in the Feat full model setup is it the same to 1)
> > consider the baseline condition as en EV and contrast it with the
> > main condition; 2) just omit the baseline and FSL will contrast it
> > with all the EV's?
> > I ask this because I tried both options and results are very
> > similar, although not absolutely equal.
> > Thanks in advance.
> > Carlos
>
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