Many thanks for your help. I tried to set up the design matrix as
suggested (see
below) with 11 subjects x 4 scans I have 44 evs. When I try to enter 44 evs I
get an error in the design matrix (GLM)window; I get a grey section in the
window for the the first 19 inputs. It appears that I can only enter a maximum
of 35 evs. Has anyone had this problem before?
Many thanks.
Alison
Quoting Mark Woolrich <[log in to unmask]>:
> Hi Alison,
>
> I would do this in 3 levels. Do a fixed effect analysis at the second
> level, which estimates separate contrasts for all of the individual
> subject before and after differences, e.g.:
>
> subj1 before treat -1 1 0 0 0 0 0 0 ...
> after treat 1 1 0 0 0 0 0 0 ...
> before cont 0 0 -1 1 0 0 0 0 ...
> after cont 0 0 1 1 0 0 0 0 ...
> subj2 before treat 0 0 0 0 -1 1 0 0 ...
> after treat 0 0 0 0 1 1 0 0 ...
> before cont 0 0 0 0 0 0 -1 1 ...
> after cont 0 0 0 0 0 0 1 1 ...
> etc...
>
> contrast1(sub1,treat) 1 0 0 0 0 0 0 0
> contrast2(sub1,cont) 0 0 1 0 0 0 0 0
> contrast3(sub2,treat) 0 0 0 0 1 0 0 0
> contrast4(sub2,cont) 0 0 0 0 0 0 1 0
>
> etc...
>
> Note that you need EVs that model the individual (treatment or
> control) subject means.
>
> The at a third level do a mixed effect analysis for a control-
> treatment paired difference (see http://www.fmrib.ox.ac.uk/fsl/feat5/
> detail.html#PairedTwoGroupDifference for inspiration) between
> appropriate subjects' contrasts from the second level:
>
> contrast1(sub1,treat) 1 1 0 ...
> contrast2(sub1,cont) -1 1 0 ...
> contrast3(sub2,treat) 1 0 1 ...
> contrast4(sub2,cont) -1 0 1 ...
> etc...
>
> contrast 1 0 0 ...
>
> Best regards, Mark.
>
> ----
> Dr Mark Woolrich
> EPSRC Advanced Research Fellow University Research Lecturer
>
> Oxford University Centre for Functional MRI of the Brain (FMRIB),
> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
>
> Tel: (+44)1865-222782 Homepage: http://www.fmrib.ox.ac.uk/~woolrich
>
>
>
>
> On 25 Apr 2007, at 14:51, Alison Watson wrote:
>
>> I have 11 subjects each had 2 scanning sessions a treatment session
>> and a control session. During each session subjects has 2 separate
>> scans one pre drug and one post drug. I want to do the following
>> contrast
>>
>>
>>
>> [treatment (post - pre) – control(post-pre)] to image treatment
>> increases related to control and [control (post - pre) – treatment
>> (post-pre)] to image treatment decreases relative to control. I am
>> not sure how to set up the design matrix. Can anyone help please?
>>
>>
>>
>> Many thanks
>>
>>
>>
>> Alison
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
--
Alison Watson
Human Pain Research Group
Clinical Sciences Building
Hope Hospital
Salford
UK
M6 8HD
Tel 0161 206 4529
www.hop.man.ac.uk/painresearch
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