Hi,
If you are running a separate higher-level analysis on each of the
lower-level contrasts/conditions, without contrasting between them,
then it is best and simplest to indeed run each of these separately.
However, if you do need to combine lower-level results in a more
complicated way you need a more complicated higher-level design.
Sorry I can't be more specific but I would need to know exactly what
kind of design you have in mind.
Cheers, Steve.
On 10 Jul 2007, at 00:35, Vinod Venkatraman wrote:
> 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
>> ---------------------------------------------------------------------
>> ---
>> ---
>> =====================================================================
>> ====
------------------------------------------------------------------------
---
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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