Dear Thilo (anybody else welcome),
Thank you for your reply. To clarify:
1) what does the contrast I suggested then exactly test for? (You said
"compare a reduced model to the full one")
2) what does
[-1 1;
-1 1]
versus
[-1 1 -1 1] test for?
Thank you again!
Helmut
> Dear Helmut,
> I guess your contrasts compare a reduced model to the full one, which is
> probably not what you want. To find out differences between conditions
> irrespective of their signs I think it's appropriate to specify the
> contrast-
> "matrix" for the F-test as if it were a t-contrast, i.e:
> [-1 1] or
> [-1 1 -1 1]
> but still doing an F-test.
>
> Please correct me, if I'm wrong....
> Thilo
>
> On Tuesday 20 September 2005 19:47, Helmut Laufs wrote:
>> Dear SPMers,
>>
>> to test whether there is any difference (i.e. irrespective of the
>> direction
>> of signal change) between two conditions, is it valid to do an F contrast
>> like this:
>>
>> [-1 0;
>> 0 1]
>>
>> ?
>>
>> ..and extending this to two sessions (repeated conditions) in one design
>> (let's assume, there are only 2 conditions/colums per session):
>>
>> [-1 0;
>> 0 1;
>> 0 0 -1;
>> 0 0 0 1]
>>
>> ?
>>
>> It looked straight forward to me in the first place, but now I am
>> confused.
>>
>> Any help appreciated.
>>
>> Thank you.
>>
>> Helmut
>
> --
> Thilo Kellermann
> RWTH Aachen University
> Pauwelstr. 30
> 52074 Aachen
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>
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