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Yes, that seems like a useful approach. I've been experimenting along those lines! -----Original Message----- From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of Jason Steffener Sent: 17 March 2012 13:07 To: [log in to unmask] Subject: Re: [SPM] Missing voxels Hello. I agree that this is an important issue that needs more discussion. I have often thought that a degrees of freedom map could be used. So instead of assuming you have a fixed dof across the brain one would have dof that vary. This of course complicates interpretation but results could be reported based on height of significance for all voxels with dof greater than some value. And as research studies are starting to use larger and larger number of subjects, I feel this approach is starting to become more viable. Now how this would affect cluster extents and thresholds is another issue. This approach is possible, but only with some coding. Jason On Sat, Mar 17, 2012 at 8:47 AM, Elizabeth Liddle <[log in to unmask]> wrote: > When a study involves a large number of participants, the cumulative > effect of a few voxels masked out in each subject at 2nd level > analysis can lead to a very small group mask, even though for any one > voxel only a small number of subjects may have missing data. To make > matters worse, often missing voxels are towards the edge of the image, > meaning that the result composite mask is lacking the regions of > greatest interest - the cortex near the skull. > > > > One solution, obviously, is to use an explicit mask, and another is to > over-ride the default threshold of .8 for voxel inclusion at first > level, but these solutions means that voxels that are, by definition, > noisy, will be included. Do people on the list have any solutions to this problem? > > > > Elizabeth > > > > ______________________________________________________________________ > _______ > > Dr Elizabeth Liddle > > Lecturer in Translational Mental Health > > Division of Psychiatry > > E Floor, South Block > > Queen's Medical Centre > > University of Nottingham > > NG11 2UH > > UK > > Tel: +44 (0)115 74 84013 > > > > > This message and any attachment are intended solely for the addressee > and may contain confidential information. If you have received this > message in error, please send it back to me, and immediately delete > it. Please do not use, copy or disclose the information contained in > this message or in any attachment. Any views or opinions expressed by > the author of this email do not necessarily reflect the views of the University of Nottingham. > > This message has been checked for viruses but the contents of an > attachment may still contain software viruses which could damage your computer system: > you are advised to perform your own checks. Email communications with > the University of Nottingham may be monitored as permitted by UK legislation.