Dear Molly,
You have a mixed design with a between subject factor (group) and a
within subject factor (condition) so have a look in previous emails when
to use a full factorial design and when to use a flexible factorial
design (to model subject effects).
Apart from that, your contrasts seem fine - you would indeed enter them
as separate t or F contrasts.
An alternative would be to compute the average or differential effect of
condition for each subject and enter these new contrast images in one or
two sample t-tests designs depending on whether you are testing for main
effects or interactions.
Best regards,
Guillaume.
On 11/01/17 22:59, Molly Memel wrote:
> I am trying to create a 2x2 full factorial design with group (young, old) and condition (Combined, Separated) in spm8. I have read through multiple manuals and can't seem to grasp how to correctly enter the contrasts for this design.
>
> I know that if I set up the design as A1C1, A1C2, A2C1, A2C2, the appropriate contrasts are as follows:
> (F) Main effect of Age: 1 1 -1 -1
>
> (F): main effect of condition: 1 -1 1 -1
>
> (F) Interaction of age x condition : 1 -1 -1 1
>
> However, do I enter those all at the same time?
>
> For example as, [ 1 1 -1 -1,
>
> 1 -1 1 -1,
>
> 1 -1 -1 1]
>
> Or do you enter each effect separately as a unique contrast?
>
> Any help would be much appreciated!
>
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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