Given the different time distances, the best would be mixed effects models. The 2 stage model should also work as it incorporates time (but not different correlations according to time distance).
Again I don't see what you are analyzing with only one group. There will always be thinning, and you will find it in some regions more than in others (depending on how much power you have). Best Martin Sent via my smartphone, please excuse brevity. -------- Original message -------- From: amirhossein manzouri <a.h.manzo...@gmail.com> Date:01/31/2014 7:27 AM (GMT-05:00) To: Martin Reuter <mreu...@nmr.mgh.harvard.edu> Cc: Douglas Greve <gr...@nmr.mgh.harvard.edu>,free surfer <freesurfer@nmr.mgh.harvard.edu> Subject: Re: [Freesurfer] Longitudinal analysis within one group Dear Doug and Martin, Thanks a lot. I just have one group including 20 subjects. The scans have been done in a range of 0.9 to 1.5 years difference (tp2-tp1). Is ooh if I use the instructions from Paired Analysis :https://surfer.nmr.mgh.harvard.edu/fswiki/PairedAnalysis ? Regards, Best regards, Amirhossein Manzouri On Thu, Jan 30, 2014 at 10:31 PM, Martin Reuter <mreu...@nmr.mgh.harvard.edu> wrote: Hi, with one group you want to check if atrophy is significantly different from zero? That is probably the case for any group (e.g. aging), so it won't tell you anything really. Also, if you don't find atrophy in a region it doesn't mean it's not there (only your group size is too small to detect it). So the only real use I can think of, would be a test-retest study, where the assumption is that there is no change? Sadly Qdec cannot do 'one sample group mean', otherwise you could do that in qdec. If only you had a second 'control' group, then it could be done. You can use long_mris_slopes to compute rate or percent change maps (one for each subjects) and then you can use qdec to analyze those rate maps across groups. If you don't have a control group, you could still use long_mris_slopes (it can also map and stack the rate maps on fsaverage) and then simply run the one sample group mean in mri_glmfit. some info is also here: https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/LongitudinalTutorial_freeview and https://surfer.nmr.mgh.harvard.edu/fswiki/LongitudinalTwoStageModel Best, Martin On 01/30/2014 09:18 AM, amirhossein manzouri wrote: Hi, Would you please advise if it is possible to do longitudinal statistical analysis within a group with two time points in Qdec. And if it is not possible in Qdec how I suppose to do it? Best regards, Amirhossein Manzouri _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Martin Reuter, Ph.D. Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT A.A.Martinos Center for Biomedical Imaging 149 Thirteenth Street, Suite 2301 Charlestown, MA 02129 Phone: +1-617-724-5652 Email: mreu...@nmr.mgh.harvard.edu reu...@mit.edu Web : http://reuter.mit.edu The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
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