Dear Gaby,
I'll let the stats gurus confirm but in principle if your analysis leads to you looking at the same volume the stats should be the same.
While I'm all for hypothesis driven research and looking at small volumes, I would personally still prefer your first option. This is because looking at the full SPM may give you more information. For example, you get a feel for edge artefacts in comparisons which may not be apparent when checking normalisation. In addition, in epilepsy but I guess in other patient populations as well, nonsignificant blobbies all over the place may be more prevalent than in control/control comparisons - if we all stare hard enough for long enough, it all may become a pattern and make sense. In summary, while the SVC toolbox will keep your stats neat, why throw away all the other information?
For an example of how we've gone about the problem in TLE, you could check Hammers A et al. Brain 2002.
All the best,
Alexander
----------------------------
Dr Alexander Hammers, MD PhD
MRC Clinician Scientist Fellow
Honorary Clinical Lecturer
Clinical Sciences Centre
Room 243, MRC Cyclotron Building
Faculty of Medicine, Imperial College London
Hammersmith Hospital, DuCane Road, London W12 0NN
and
Honorary Lecturer in Neurology
Department of Clinical and Experimental Epilepsy
National Hospital for Neurology and Neurosurgery/ Institute of Neurology,
UCL
33 Queen Square, London WC1N 3BG
Telephone +44-(0)20-8383-3162 (ext./direct line -3704 or -2651)
Fax +44-(0)20-8383-1783 /-2029
Email [log in to unmask], [log in to unmask]
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]On
Behalf Of Gaby Pell
Sent: 12 January 2005 09:23
To: [log in to unmask]
Subject: Re: [SPM] small volume correction
Dear SPM users,
What is the statistical difference between the following three approaches
for small volume correction:
(1) use of the SVC toolbox
(2) explicit masking in SPM with the volume of interest
(3) (even simpler) masking the data set with the VOI before implementing a
standard SPM analysis
Thanks,
Gaby
***************************************
Gaby Pell, PhD
Brain Research Institute
Ground Floor, Neurosciences Building
Austin & Repatriation Medical Centre
Banksia Street
West Heidelberg,
Melbourne,
Victoria, 3081
Australia
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