Hi - no, sqrt(VARCOPE) will be in the same units as COPE - if you want
errorbars on the %SC then you'd do the same maths on the sqrt(VARCOPE)
as for the COPE.
Cheers.
On 22 Nov 2007, at 11:32, Martin M Monti wrote:
> Steve, thank you. Only one question, when you say you'd use
> sqrt(VARCOPE) as "error-bars on the COPE" you mean the %SC
> transformed COPE?
>
> cheers
>
> martin
>
> Steve Smith wrote:
>> Hi - yes, this is straightforward:
>>
>> %SC = 100 * COPE * H / mean_func
>>
>> where H is the peak-peak-height equivalent for the relevant
>> contrast, found in the header of design.con (see the estimability
>> paper for more details on this).
>>
>> I would think you would want to just use sqrt(varcope) as errorbars
>> on the cope.
>>
>> Cheers.
>>
>>
>>
>> On 21 Nov 2007, at 21:39, Martin M Monti wrote:
>>
>>> Dear FSLers,
>>>
>>> I know this has been asked in the past but i couldn't seem to find
>>> a clear answer on the FSL website (please point me towards it if I
>>> missed it..).
>>> How do I convert higher-level cope (or pe) into % signal change?
>>>
>>> I know it has to do with the design, in my case I used a slow
>>> event related in which the regressor height was always 1, and
>>> events are sufficiently spaced in time that the amplitude of one
>>> should not be affected by the preceding trial (about 14 sec
>>> fixation in between each..)
>>>
>>> Also, is it correct to use, as errorbars for the cope the varcope/
>>> sqrt(dof)?
>>> On the other hand, how do I get errorbars when computing the
>>> average % signal change (as I was asking above)?
>>>
>>> cheers
>>>
>>> martin
>>
>>
>> ---------------------------------------------------------------------------
>> 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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