Hi,
> My question is to extend this to 3 conditions, A, B, and C, say for 5
> subjects. So should I have first three EVs model the pair-wise
comprisons
> between any two conditions AB, AC, and BC, and then another 5 EVs model
> the subject mean effect, as below? Thanks.
>
> Group EV1 EV2 EV3 EV4 EV5 EV6 EV7 EV8
> 1 1 1 0 1 0 0 0 0
> 1 1 1 0 0 1 0 0 0
> 1 1 1 0 0 0 1 0 0
> 1 1 1 0 0 0 0 1 0
> 1 1 1 0 0 0 0 0 1
> 1 -1 0 1 1 0 0 0 0
> 1 -1 0 1 0 1 0 0 0
> 1 -1 0 1 0 0 1 0 0
> 1 -1 0 1 0 0 0 1 0
> 1 -1 0 1 0 0 0 0 1
> 1 0 -1 -1 1 0 0 0 0
> 1 0 -1 -1 0 1 0 0 0
> 1 0 -1 -1 0 0 1 0 0
> 1 0 -1 -1 0 0 0 1 0
> 1 0 -1 -1 0 0 0 0 1
I think that is pretty much the way to go. However, as it stands it is
rank defficient: EV1-EV2+EV3=0.
So you need delete EV3 and getting its paired difference with a
[-1 1 0 0 0 0 0] contrast:
EV1 EV2 EV3 EV4 EV5 EV6 EV7
1 1 1 0 0 0 0
1 1 0 1 0 0 0
1 1 0 0 1 0 0
1 1 0 0 0 1 0
1 1 0 0 0 0 1
-1 0 1 0 0 0 0
-1 0 0 1 0 0 0
-1 0 0 0 1 0 0
-1 0 0 0 0 1 0
-1 0 0 0 0 0 1
0 -1 1 0 0 0 0
0 -1 0 1 0 0 0
0 -1 0 0 1 0 0
0 -1 0 0 0 1 0
0 -1 0 0 0 0 1
Cheers, Mark.
Mark Woolrich.
Oxford University Centre for Functional MRI of the Brain (FMRIB),
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
Tel: (+44)1865-222782 Homepage: http://www.fmrib.ox.ac.uk/~woolrich
On Tue, 11 May 2004, X Liu wrote:
> +++From feat5.pdf+++
> Paired Two-Group Difference (Two-Sample Paired T-Test)
> We have a group of 8 subjects scanned under two different conditions, A and
> B. We enter the condition A analyses as the first 8 inputs, and the
> condition B analyses as the second 8 inputs. Make sure that the subjects
> are in the same order within each group of 8! We need one EV for the A-B
> differences, and then one extra EV for each subject, making 9 in all. EVs 2-
> 9 model each subject's mean effect - in this analysis this is a confound,
> i.e. parameter estimates 2-9 are ignored, but without this part of the
> model, the mean effects would intefere with the estimation of the A-B
> paired differences. A contrast with a one for EV1 and zeros elsewhere tests
> for A-B paired differences.
> ++++++++++++++++++++
>
> My question is to extend this to 3 conditions, A, B, and C, say for 5
> subjects. So should I have first three EVs model the pair-wise comprisons
> between any two conditions AB, AC, and BC, and then another 5 EVs to model
> the subject mean effect, as below? Thanks.
>
> Group EV1 EV2 EV3 EV4 EV5 EV6 EV7 EV8
> 1 1 1 0 1 0 0 0 0
> 1 1 1 0 0 1 0 0 0
> 1 1 1 0 0 0 1 0 0
> 1 1 1 0 0 0 0 1 0
> 1 1 1 0 0 0 0 0 1
> 1 -1 0 1 1 0 0 0 0
> 1 -1 0 1 0 1 0 0 0
> 1 -1 0 1 0 0 1 0 0
> 1 -1 0 1 0 0 0 1 0
> 1 -1 0 1 0 0 0 0 1
> 1 0 -1 -1 1 0 0 0 0
> 1 0 -1 -1 0 1 0 0 0
> 1 0 -1 -1 0 0 1 0 0
> 1 0 -1 -1 0 0 0 1 0
> 1 0 -1 -1 0 0 0 0 1
>
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