Dear Alle
spm_mfx could be the program you are looking for here differences in
first level analysis is accounted for. The article describing the
method is now accepted for publication in NeuroImage.
Best
Torben E. Lund
Danish Research Centre for MR
Copenhagen University Hospital
Kettegaard Allé 30
2650 Hvidovre
Denmark
email: [log in to unmask]
webpage: http://www.drcmr.dk
On 9/11-2004, at 16.48, Alle Meije Wink wrote:
> Hello Christian and others,
>
> I have recently had similar discussion about the .con images. Even
> apart
> from differences in global scaling, should the .con images not be
> normalised/equalised with respect to the temporal variance? If the
> first-level contrast images are computed from time series with very
> different temporal variances, is it possible to just use them in a
> standard statistical test on the 2nd level? And would it be possible to
> solve this by doing the unit variance step (dividing by the values in
> the ess images) before enterinig the 2nd level?
>
> In other words, does the term `mixed effects' also apply when the
> subjects have been drawn from different populations (regarding their
> temporal variance)?
>
> The most kosher solution would probably be a nonparametric 2nd-level
> analysis (if all .con-images have different variances, there is not one
> unique value for the variance parameter). SnPM can be used for this
> step.
>
> This List message speaks about `homogeneous intrasubject' variance.
> That
> is all I have found so far...
> http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0407&L=spm&P=R17622&I=-1
>
> One other about temporal autocorrelations (which may be related)
> http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0303&L=spm&P=R6147&I=-1
>
> With best regards,
> Alle Meije Wink
>
> Christian Keysers wrote:
>> Dear SPM community,
>>
>> When using subject by subject first level analysis, and bringing the
>> con*.img to the second level, a colleague of mine asked me the
>> seemingly
>> simple question of how scaling is handled. Not being scaled in a
>> single
>> design matrix, are the beta values comparable enough? What if the
>> different subjects have dramatically different global's? Any
>> reactions?
>>
>> Christian
>
> --
>
> Brain Mapping Unit
> Dept. of Psychiatry
> University of Cambridge
> Addenbrooke's Hospital
> Cambridge CB2 2QQ
>
> Tel: +44 (0)1223 336963
> Fax: +44 (0)1223 336581
>
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