Hi Omar,
these two contrasts (for instance):
1 -1 -1 1 0 0
1 -1 0 0 -1 1
Cheers,
Gwenaëlle
--- En date de : Jeu 28.1.10, Omar Alhassoon <[log in to unmask]> a écrit :
> De: Omar Alhassoon <[log in to unmask]>
> Objet: Re: [FSL] Randomize design and contrast matrix for Fractional Anisotropy
> À: [log in to unmask]
> Date: Jeudi 28 Janvier 2010, 20h36
> Thank you Matthew and Gwenaelle,
>
> I have been trying to figure how to set up an F-test in Glm
> that would
> test the omnibus question of whether there is an
> interaction between
> time and group in a 2x3 design. I understand that I need to
> set up
> some contrasts, set the F button to 1, then click on the
> buttons next
> to the contrasts that I want to include in the F-test. But
> I have no
> idea what contrasts should be included in such a design.
> Any
> suggestions.
>
> Thanks again,
> Omar
>
> On Thu, Jan 28, 2010 at 12:11 PM, Matthew Webster
> <[log in to unmask]>
> wrote:
> > Hello,
> > If you are using the group column in the GLM to
> set up a design.grp
> > file for use with the -e option in randomise, you can
> safely ignore
> > this message.
> >
> > Many Regards
> > Matthew
> >> Thank you for your response, it is very
> re-assuring.
> >>
> >> With regards to the error messages you said:
> >>
> >>>It is probably because you've run exactly the
> model above that is
> >>>indeed rank deficient. You just need to add
> some subjects (and
> >>>presumably you've got more than one control) as
> some additional EVs and
> >>>it should not be a problem anymore...
> >>
> >> Actually, I have run this model in Glm using 24
> controls, 15 abstinent
> >> subjects, and 5 relapsers. That is when the error
> message appears. So,
> >> adding the EVs in the same way I did with the
> example dataset does not
> >> seem to resolve this error message. Do you have
> other thoughts about
> >> why this could be happening?
> >>
> >> Thank you so much.
> >> Omar
> >>
> >>
> >>
> >>
> >>> Problem with processing the model. Warning: at
> least one EV is (close
> >>> to) a linear combination of the others. You
> probably need to alter
> >>> your design. (Design matrix is rank deficient
> - ratio of min:max
> >>> eigenvalues in SVD of matrix is 1.21792e-17).
> >>>
> >>> Warning-design matrix uses different groups
> (for different variances),
> >>> but these do not contain "separable" Evs for
> the different groups (it
> >>> is necessary that, for each EV, only one of
> the groups has non-zero
> >>> values).
> >>
> >> Hope this helps,
> >> Gwenaelle
> >>
> >>
> >
>
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