Hello Mayuresh,
your approach looks perfectly valid to me. Good luck with your analysis.
Best regards
Raphael
Am 21.06.2011 07:20, schrieb Mayuresh K:
> Hello SPMers,
>
> I am working on data from three fMRI tasks for two groups of subjects.
> The two groups are significantly different in several brain areas for
> individual group analyses for each of the 3 tasks. I am interested in
> identifying if there is an overlap in brain regions (with
> group1>group2) across the three tasks. I would appreciate if someone
> can review my model setup and validate if this approach is correct?
>
> I have setup this analysis using a "Flexible factorial model" with
> factors:
> 1. subject (independence, equal variance) ;
> 2. group (independence, unequal variance) and
> 3. task (dependent, equal variance).
>
> I have specified all the subjects such that:
> 1. each subject belonging to group 1 has a factor matrix: [1, 1; 1, 2;
> 1, 3]
> 2. each subject belonging to group 2 has a factor matrix: [2, 1; 2, 2;
> 2, 3]
> i.e. first row for group membership & second row for task.
>
> Main Effect: subject
> Interaction: [2 3] i.e. group by task
>
> The resulting design matrix has the following columns: N1 + N2 + 3
> task columns group 1 + 3 task columns group 2. (N1&N2 are number of
> subjects in group1 and group2 resp)
>
> I have defined three contrasts - one for each task (group1>group2):
> 1. task 1 - ones(1,N1)/N1 -ones(1,N2)/N2 1 0 0 -1 0 0
> 2. task 2 - ones(1,N1)/N1 -ones(1,N2)/N2 0 1 0 0 -1 0
> 3. task 3 - ones(1,N1)/N1 -ones(1,N2)/N2 0 0 1 0 0 -1
>
> to achieve the conjunction, I select all the three contrasts for
> interrogation.
> Is this a valid approach?
>
> Thanks,
> Mayuresh
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