(1) I think subject should be set to equal variance AND it needs to be
in the model.
(2) Some of the conjunctions are impossible, some are possible, here is why:
A1: 1 1 0 0
B1: 1 0 1 0
A2: 0 0 1 1
B2 0 1 0 1
A1>B1: 0 1 -1 0
A2>B2: 0 -1 1 0
The conjunction of these two is 0 since they can't overlap!!!
A1>A2: 1 1 -1 -1
B1>B2: 1 -1 1 -1
The conjunction of these two is possible since they can overlap.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
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On Tue, Sep 13, 2011 at 5:07 AM, Cyril Pernet <[log in to unmask]> wrote:
> Hi Bob
>
> looks ok - once you 'run' make sure the subjects factors appear in the
> design matrix (as the factor_matrix.png only showed the factors)
> conjunctions will be between contrasts 1 0 -1 0 & 0 1 0 -1 and between 1 -1
> & 1 -1
>
> Hope this helps
> Cyril
>
>
>> Dear SPM experts,
>>
>> I am trying to setup a group-level model to test the conjunction of
>> simple effects. Namely, I have a 2 X 2 within-subjects factorial
>> design, with factors A (two levels, A1 and A2) and B (two levels, B1
>> and B2). My current understanding is that it is most appropriate to
>> model this using a flexible factorial design, with the following
>> factors:
>>
>> 1. Subject
>> 2. Factor A
>> 3. Factor B
>>
>> I've used the attached parameters (pictured in params.png) and factor
>> matrix (pictured in factor_matrix.png). As you can see, I've defined
>> only the interaction among A and B. In this model, my primary interest
>> is in interrogating the conjunction of the simple effects, e.g. A1>
>> B1& A2> B2, and also A1> A2& B1> B2.
>>
>> Is this model correct? I realize this may be a simple-minded question,
>> but I'm still living in the days of the one-sample t-test and am
>> unsure about how to appropriately use the flexible factorial model.
>>
>> Sincerely,
>>
>> Bob Spunt
>> Postdoctoral Fellow
>> Social Cognitive Neuroscience Lab - www.scn.ucla.edu
>> Department of Psychology
>> University of California, Los Angeles
>
>
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