Hi - I'm still a little confused as we never call this "efficacy" -
this is a plot of the eigenvalues from a singular value decomposition
of the design matrix - it's not as directly useful or interpretable as
the "Effect required" efficiency calculations - if they look ok then
that's good enough.
Cheers.
On 1 Jun 2008, at 23:29, Jose Paulo Santos wrote:
> Hello,
>
> Yes, I got these values from FEAT (please see attachment; this
> example is
> for 250 volumes). The Efficacy is the right most value in the
> diagonal (I
> didn’t consider the others) and the Mean Effect Required is the mean
> of
> Ci’s.
>
> Kind regards,
> Jose Paulo Santos
>
>
> On Fri, 30 May 2008 08:19:03 +0100, Steve Smith <[log in to unmask]>
> wrote:
>
>> Hi - I'm not sure where these Efficacy numbers come from - not from
>> the FEAT efficiency calculations I think? I'm not sure what these
>> are.......
>> Cheers.
>>
>>
>>
>> On 28 May 2008, at 19:10, Jose Paulo Santos wrote:
>>
>>> Hello,
>>>
>>> I'm trying to establish some kind of method to achieve to the
>>> optimal
>>> length in event-related paradigms.
>>>
>>> I designed a paradigm were I collected 500 volumes. The participant
>>> reported at the end that he was exhausted. So I know that 500
>>> volumes were
>>> too much in the human perspective. By the end of the session, the
>>> probability of the participant still being concentrated in the task
>>> was
>>> quite low.
>>>
>>> With fslsplit and fslmerge commands, I reconstructed several files,
>>> until
>>> 250 volumes, and I analyzed each of them with Feat. The numerical
>>> data was:
>>>
>>> Volumes Efficacy Mean Effect Required
>>> 250 0.253 0.938
>>> 312 0.241 0.847
>>> 375 0.251 0.752
>>> 438 0.245 0.740
>>> 500 0.243 0.722
>>>
>>> The rule of thumb for the Efficacy determines that it must be more
>>> than
>>> 0.200, and it was for all volumes. The rule of thumb for the Effect
>>> Required determines that it must be less than 0.800. This
>>> requirement is
>>> true only for 375 volumes or more. When this data is plotted, it
>>> seems
>>> that there aren’t significant increases in the Effect Required for
>>> more
>>> than 375 volumes. This is in line when the maps are analyzed: the
>>> 375
>>> volumes map has activations more intense (just a bit) and more
>>> extended
>>> (just a bit) than the 438 and 500 maps. So, 375 volumes would be the
>>> optimal length (and duration) of the session. If there is some
>>> clearance,
>>> it would be better to increase the inter stimulus interval (null
>>> event)
>>> than to show more stimuli.
>>>
>>> Is this acceptable? Why the Efficacy didn’t change so much?
>>> Increasing
>>> ISIs would increase the Efficacy?
>>>
>>> Thanks in advance,
>>> Jose Paulo Santos
>>>
>>
>>
>> --------------------------------------------------------------------------
> -
>> 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
>> --------------------------------------------------------------------------
> -
>> =
>> =
>> =
>> =====================================================================
> <design_cov.png>
---------------------------------------------------------------------------
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
---------------------------------------------------------------------------
|