On Nov 18, 2008, at 12:11 PM, J Labus wrote:
> I have 2 groups of subject who underwent 4 conditions in an fMRI
> study. I
> want to show where activation in these 4 conditions correlates with a
> continuous variable. I have an average measure of the continuous
> variable
> for each subject in each condition. I have been struggling to
> specify the
> appropriate second-level design.
>
> I chose 'full factorial" design and specified the scans representing
> activity for each condition in each group. I specified group and
> condition
> as factors (8 total factors). I also specified the 1 covariate.
>
> The design does not produce the results I expected. I get a F
> tests for
> 1)avg effect of condition, 2)main effect of group,3) main effect for
> condition, and 4) interaction between group and condition.
> However, the
> main effect of the covariate is not shown in the results manager.
>
>
> It seems that the authors of SPM have chosen not to report the F
> test of the
> beta for the covariate in the results( although of course it has been
> estimated). So if this is correct, what model should I be employing to
> answer my question.
>
> Is it multiple regression? If so, if so i need to clarify 2 things.
> 1)Do i
> need 8 covariates with values for each relevant cell and zeros for
> the 7
> other cells? Do i need to center the covariate across the 8
> conditions ahead
> of time?
>
> Thank you for any help you can provide,
> Jen
>
>
>
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