Hi,
On 18 Jul 2008, at 18:40, Russell Chu wrote:
> Thanks Steve and Gwenaelle, I really appreciate your help! So with
> my new
> design matrix below, what would the contrast matrices look like if I
> want to
>
> 1) find the effect of age on the differences in average FA
Not sure what you mean - are you saying that the groups are not age-
matched?
> 2) remove the effect of age
>
> The ages of the controls were demeaned ONLY by the mean age of the
> controls.
> The ages of patients were demeaned ONLY by the mean age of the
> patients.
Correct.
Cheers
>
>
> Design matrix:
> EV1(control) EV2(patient) EV3(ageControlDemeaned)
> EV4(agePatientDemeaned)
> 0 1 0 4
> 0 1 0 -2
> ...
> ...
> 1 0 3 0
> 1 0 -1 0
>
> randomise -i all_FA_skeletonised -o tbss -m mean_FA_skeleton_mask -d
> design.mat -t design.con -n 500 -c 3 -D -V
>
> Thanks so much for your time and patience!
>
> Cheers,
> Russell
>
> -----Original Message-----
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]]On
> Behalf Of Steve Smith
> Sent: Thursday, July 17, 2008 7:14 AM
> To: [log in to unmask]
> Subject: Re: [FSL] age and age*group interaction for randomise and
> tbss
>
>
> Hi,
>
> The problem is that the design is rank deficient - at least one EV is
> a linear combination of others. I would use the following design:
>
>
> EV1(control) EV2(patient) EV3(demeanedagecontrol)
> EV4(demeanedagepatient)
> 1
> 0
> 3 0
> 1
> 0
> -3 0
> 0
> 1
> 0 4
> 0
> 1
> 0 -4
>
> and e.g. a contrast [0 0 1 -1] asks for (one direction of) the age
> interation.
>
> Cheers.
>
>
>
> On 16 Jul 2008, at 20:20, Russell Chu wrote:
>
>> Hi,
>> I processed some patients and controls with TBSS and am now trying
>> to find
>> the age effect and age*group interaction in randomise. Would someone
>> please
>> check my design and contrast matrices below? Also, in the design
>> matrix, I
>> subtracted the mean age from each individual subject's age; is this
>> the
>> proper way to demean the ages?
>>
>> Design matrix:
>> EV1(control) EV2(patient) EV3(age) EV4(age*control) EV5(age*patient)
>> 1 0 4 4 0
>> 1 0 -4 -4 0
>> 0 1 -9.8 0 -9.8
>> ...
>> ...
>> 0 1 -1.2 0 -1.2
>> 0 1 -3 0 -3
>> 1 0 -4 -4 0
>> 1 0 4.3 4.3 0
>>
>> Contrast matrix:
>> EV1(control) EV2(patient) EV3(age) EV4(age*control) EV5(age*patient)
>> control>meth 1 -1 0 0 0
>> meth>control -1 1 0 0 0
>>
>> randomise -i all_FA_skeletonised -o tbss -m mean_FA_skeleton_mask -d
>> design.mat -t design.con -n 100 -c 3 -V
>>
>> Also, after all permutations (only 100 for quick initial results) are
>> finished, the following error occurs:
>>
>> terminate called after throwing an instance of
>> 'NEWMAT::ConvergenceException'
>> Aborted
>>
>> Any input on these issues would be greatly appreciated.
>>
>> Thanks,
>> Russell
>>
>
>
> ---------------------------------------------------------------------------
> Stephen M. Smith, Professor of Biomedical Engineering
> Associate Director, Oxford University FMRIB Centre
>
> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> +44 (0) 1865 222726 (fax 222717)
> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
> ---------------------------------------------------------------------------
>
---------------------------------------------------------------------------
Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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