Fantastic. Thank you for clarifying this point. I'm sure I'm not alone in my
anticipation for the next release. Thanks again!
-Jim
On Wed, 8 Aug 2007 16:48:51 +0100, Steve Smith <[log in to unmask]> wrote:
>Hi - yes, you're right - after many debates we've mostly been
>convinced (thanks Jesper ;-) that the right second-level within-
>subject cross-session modelling is FE - hence this recommendation is
>changing for the new release...sorry should have made that
>clearer...the new FEAT manual will explain the logic.....
>
>Cheers, Steve.
>
>from the new manual:
>
>"If you are carrying out a mid-level analysis (e.g., cross-sessions)
>and will be feeding this into an even higher-level analysis (e.g.,
>cross-subjects), then you should not use the FLAME 1+2 option, as it
>is not possible for FLAME to know in advance of the highest-level
>analysis what voxels will ultimately be near threshold. In fact, in
>such situations, you should probably use FE (fixed effects) for the
>mid-level analysis, with a separate FE analysis for each subject.
>This in effect treats the multiple first-level sessions (for each
>subject) as if they were one long session, and ignores the session-
>session variability (which arguably is not of interest, and which you
>never model explicitly if you only took just one session for each
>subject). This approach also avoids the problem of having to pool
>second-level variance across subjects, in the case where you don't
>have many sessions for each subject. Finally, it does not seem to
>make much sense that a ME cross-session analysis leaves you less
>certain about the combined within-subject-across-session results than
>if you have just analysed one of the first-level sessions - hence FE
>makes more sense."
>
>
>
>
>On 8 Aug 2007, at 16:20, James Porter wrote:
>
>> Hello-
>>
>> I'm a little confused by this answer. I was under the impression
>> that using
>> FE analyses to combine single-subject sessions was a dead-end as
>> far as
>> group analyses go. The FEAT Details web page states,
>>
>> "Also note that you should probably not feed up second-level
>> FE analyses to higher-level analyses; you should use a full
>> mixed-effects analysis at all levels."
>>
>> Is this not counter to what is written below, or am I misreading
>> something?
>>
>> Thanks,
>>
>> Jim Porter
>> TRiCAM Lab Coordinator
>> Elliott Hall N437
>> 612.624.3892
>> www.psych.umn.edu/research/tricam
>>
>>
>> On Wed, 8 Aug 2007 07:41:19 +0100, Steve Smith
>> <[log in to unmask]> wrote:
>>
>>> Hi - I would combine across session within-subject using FE for each
>>> subject separately at second level and then feed this up into a
>>> cross-
>>> subject analysis.
>>> Cheers, Steve.
>>>
>>>
>>> On 8 Aug 2007, at 02:39, Matthew Hoptman wrote:
>>>
>>>> Hi all,
>>>> I'd like to set up an analysis in which I do a cross group
>>>> comparison on
>>>> conditions from two different tasks collected in the same scanning
>>>> session
>>>> (but in different runs). I see how to do paired t-tests, but this
>>>> is sort
>>>> of like doing a repeated measures ANOVA with a grouping variable,
>>>> and I
>>>> can't seem to get it to work out. When I set up the paired aspect,
>>>> the
>>>> groups selector seems to default to a single column. That makes it
>>>> hard to
>>>> do the grouping part.
>>>>
>>>> I guess what I'm thinking is:
>>>>
>>>> Group Patients Controls Condition S1 S2 S3
>>>> 1 1 0 1 1 0 0
>>>> 1 1 0 1 0 1 0
>>>> 1 1 0 1 0 0 1
>>>> 1 1 0 2 1 0 0
>>>> 1 1 0 2 0 1 0
>>>> 1 1 0 2 0 0 1
>>>> 2 0 1 1 1 0 0
>>>> etc.
>>>>
>>>> Any ideas?
>>>> Thanks,
>>>> Matt
>>>
>>>
>>> ---------------------------------------------------------------------
>>> ---
>>> ---
>>> 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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