Sorry, to post this again, but I am still not sure if my method is acceptable...
Thanks
Heidi 


Op 30 aug. 2013 om 20:13 heeft "Jacobs H (NP)" <[log in to unmask]> het volgende geschreven:

> Dear Tony and Christopher,
> 
> Thanks for the information.
> 
> I don't think there were large morphological changes, as the 3 measurements were done within 4 months.
> This is why only one T1 was acquired, at baseline.
> My main problem is whether the repeated measures with 3 time points in it would still be better than what I did?
> I did the dual regression and then subtracted the stage 2 files of baseline and time point 1; and of time point 1 and time point 2 (with fslmaths).
> Then I ran randomise on those subtracted files to get the statistical maps.
> So for the GLM on the subtracted maps I had 40 input files (20 young and 20 old) allowing me to enter education and grey matter.
> 
> If I wanted to use the repeated measures GLM for the three time points, I would have 120 inputs.... I would not be able to load 3 times the same GM maps or education values, as this would create problems.
> I know that the subject-specific EVs capture a part of this, but I thought maybe not everything.
> So, therefore I chose the subtraction method.
> 
> My colleague states that I should repeated measures GLM.....
> 
> Any thoughts on this?
> 
> Thanks
> Heidi
> 
> ================================================
> Dr. Heidi Jacobs
> Postdoc researcher
> Faculty of Health, Medicine and Life Sciences
> School for Mental Health and Neurosciences
> Division Cognitive Neuropsychiatry and Clinical Neurosciences
> Alzheimer Center Limburg
> [log in to unmask]
> www.maastrichtuniversity.nl
> www.heidijacobs.nl
> 
> Dr. Tanslaan 12, 6229 ET Maastricht
> P.O. Box 616, 6200 MD Maastricht, The Netherlands
> T +31 43 38 84 090 F +31 43 38 84 092
> ================================================
> ________________________________________
> Van: FSL - FMRIB's Software Library [[log in to unmask]] namens Watson, Christopher [[log in to unmask]]
> Verzonden: vrijdag 30 augustus 2013 20:06
> Aan: [log in to unmask]
> Onderwerp: Re: [FSL] Is my approach / argumentation ok or not?
> 
> I think it might be problematic if e.g. for the old group, GM changed much more/less over the course of the 3 timepoints than in the young group. In that situation including GM from timepoint 1 won't capture that. It still could be useful to include, though, as it will still capture the "baseline" GM difference between groups.
> 
> ________________________________________
> From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Tony Jiang [[log in to unmask]]
> Sent: Friday, August 30, 2013 1:52 PM
> To: [log in to unmask]
> Subject: Re: [FSL] Is my approach / argumentation ok or not?
> 
> I dont understand why you cannot correct the education and grey matter in a GLM with 3 repeated measurements. how exactly did you do in order to subtract two time points?
> Tony
> ________________________________________
> From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Jacobs H (NP) [[log in to unmask]]
> Sent: Friday, August 30, 2013 12:30 PM
> To: [log in to unmask]
> Subject: [FSL] Is my approach / argumentation ok or not?
> 
> Dear FSLers
> 
> I have resting state data of 20 old and 20 young people, measured on three different time points (before, immediately after intervention and a bit later).
> In order to analyze my data I did the following: I subtracted time 1 and time2; time 2 and time 3 and performed two-group comparisons on these differences (as mentioned on the list).
> The advantage of this procedure is that I was able to correct for education and I could add a voxel-wise covariate for grey matter (due to the age differences).
> As I only have one T1 image this seemed to be a nice solution.
> 
> One of my co-authors actually believes this model is weak and suggests that I should perform a repeated measures GLM. However, I can not correct for education and grey matter than. I know that the subject-specific EV's account for this, but I thought that this might not capture all the differences.
> 
> Could I use the approach that I used or is the repeated measures indeed a better instrument?
> 
> Thanks!
> Best
> Heidi
> 
> 
> 
> 
> ================================================
> Dr. Heidi Jacobs
> Postdoc researcher
> Faculty of Health, Medicine and Life Sciences
> School for Mental Health and Neurosciences
> Division Cognitive Neuropsychiatry and Clinical Neurosciences
> Alzheimer Center Limburg
> [log in to unmask]
> www.maastrichtuniversity.nl
> www.heidijacobs.nl
> 
> Dr. Tanslaan 12, 6229 ET Maastricht
> P.O. Box 616, 6200 MD Maastricht, The Netherlands
> T +31 43 38 84 090 F +31 43 38 84 092
> ================================================
> 
> Kessler Foundation is proud to be recognized as one of the Best Places to Work in New Jersey.
> 
> 
> 
> The information in this transmission is intended for official use of the Kessler Foundation.  It is intended for the exclusive use of the persons or entities to which it is addressed.  If you are not an intended recipient or the employee or agent responsible for delivering this transmission to an intended recipient, be aware that any disclosure, dissemination, distribution or copying of this communication, or the use of its contents, is strictly prohibited.  If you received this transmission in error, please notify the sender by return e-mail and delete the material from any computer.