Hi,
A = a + b + c
B = a -b
C = a-c
A+B+C = 3a
So yes a [1 0 0 ] contrast gives you the mean of A,B,C.
However if you just want to ignore cross-session variability you could
just use an all 1s single EV and use the fixed-effects option?
Cheers.
On 24 Nov 2008, at 22:04, Brad Goodyear wrote:
> Hi.
> I want to compute the average across three conditions for each
> subject by removing any
> differences between the conditions.
> For two conditions, I understand the EVs would be
>
> EV1 EV2
> 1 1
> 1 -1
>
> would it not, and I compute the contrast (1,0) for the average
> across the two conditions
> with any differences removed?
>
> For three conditions, is it
>
> EV1 EV2 (a) EV3 (b)
> 1 1 1
> 1 -1 0
> 1 0 -1
>
> and then compute (1,0,0) since conditions A+B+C = a+b-a-b = 0, as
> per the tripled t-test
> example?
> I then plan to average this (1,0,0) contrast across subjects to get
> the mean across
> condition with any differences between the conditions removed.
>
> -Brad
>
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