Can someone explain the rationale between doing contrasts this way a bit
more? Also does this also extend to 5 conditions and so on? I am just
looking at an easy way of combining data from 5 different conditions at the
third level. I want to run a different bunch of contrasts between them. But
having to do so many different feat analysis (one for each contrast as most
options suggest) seems redundant and if I can run them all in one analyses,
that would be great, but doing it the way proposed below does not seem very
obvious. Any help in understanding this approach will be great.
Thanks
Vinod
On Sun, 22 Oct 2006 11:22:12 +0100, Steve Smith <[log in to unmask]>
wrote:
>Sorry Brad, my mistake - you actually only need one extra EV to
>extend the main part of the design from tripled to quadrupled:
>
>
>1 1 1 1 0 0
>1 1 1 0 1 0
>1 1 1 0 0 1
>-1 0 0 1 0 0
>-1 0 0 0 1 0
>-1 0 0 0 0 1
>0 -1 0 1 0 0
>0 -1 0 0 1 0
>0 -1 0 0 0 1
>0 0 -1 1 0 0
>0 0 -1 0 1 0
>0 0 -1 0 0 1
>
>and to work out the contrasts:
>
>A = a + b + c
>B = -a
>C = -b
>D = -c
>
>A-B = 2a + b + c = [2 1 1]
>A-C = a + 2b + c = [1 2 1]
>A-D = a + b + 2c = [1 1 2]
>B-C = -a + b = [-1 1 0]
>B-D = -a + c = [-1 0 1]
>C-D = -b + c = [0 -1 1]
>etc.
>
>This should work hopefully.
>Cheers, Steve.
>
>
>
>
>On 20 Oct 2006, at 20:34, Brad Goodyear wrote:
>
>>
>> Hi Steve.
>>
>> I have tried extending the triple t-test example to do a quadruple
>> one.
>> I get a linear combination warning at the design stage, and a
>> singular matrix error upon running.
>>
>> Attached is the design file?
>> Would you be able to take a quick peek?
>>
>> Thanks,
>>
>> BRad
>>
>> <design.fsf>
>>
>>
>
>
>------------------------------------------------------------------------
>---
>Stephen M. Smith, Professor of Biomedical Engineering
>Associate Director, Oxford University FMRIB Centre
>
>FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>+44 (0) 1865 222726 (fax 222717)
>[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
>------------------------------------------------------------------------
>---
>=========================================================================
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