Hi Doug, I was wondering about something. If I have an fsgd file that has no variable set (just the 2 groups: Diseased and Control) do I need to include the DefaultVariable line at the end of the file?
Thanks, Panos > That's great. Thanks a lot for your help, Doug! > > >> >> Those are the same things. The way you control for age is to compute a >> value for both groups at the same age (eg, age=0). If you demean the >> age, then the difference will be at age=meanage. With DOSS, the >> difference is always the same regardless of age (which makes it more >> interpretable) >> doug >> >> >> On 02/25/2014 03:00 PM, pfot...@nmr.mgh.harvard.edu wrote: >>> Hi Doug, >>> >>> Thank you for your response. >>> Concerning scenario 2, I believe I have some hard time understanding >>> the >>> term intercept. If I'm not mistaken the intercept represents the >>> cortical >>> thickness at "age 0." The resulting clusters by using a design matrix >>> of >>> [1 -1 0 0] will give me the areas where the intercept is significantly >>> different between the Diseased group and the healthy group. >>> >>> Are those clusters the same clusters that have a different mean >>> regional >>> cortical thickness in Diseased versus Healthy subjects after >>> controlling >>> for age, or are those two completely different things? >>> >>> >>> Thanks again, >>> Panos >>> >>>> On 02/25/2014 02:07 PM, pfot...@nmr.mgh.harvard.edu wrote: >>>>> Hi FS community, >>>>> >>>>> I had a few questions regarding my understanding of the group >>>>> analysis >>>>> in FS: >>>>> >>>>> 1) If I use an fsgd file with Two Groups (One Factor/Two Levels), No >>>>> Covariates, and my contrast matrix is [1 -1], do the resulting >>>>> clusters >>>>> (if any) show the regional significant differences between the two >>>>> groups >>>>> by comparing just the means of the values that I am comparing? For >>>>> instance, if I'm comparing cortical thickness between a diseased and >>>>> a >>>>> control group, is this going to give me the clusters where the >>>>> Diseased >>>>> subjects' (no age included in the fsgd file, just the two groups) >>>>> mean/regional cortical thickness differs significantly from the >>>>> controls'? >>>>> In other words, is a 50 yo subject's mean/regional cortical thickness >>>>> going to be treated the same as a 80 yo subject's? >>>> Yes, just a simple two-group t-test. >>>>> 2) Now suppose that I would like to control for age. Then I'm >>>>> assuming >>>>> that I need to create an fsgd file with two Groups (One Factor/Two >>>>> Levels) >>>>> and One Covariate (age). Similarly, if I would want to visualize the >>>>> differences in the regional values of cortical thickness between the >>>>> two >>>>> groups but after they have been controlled/adjusted for age, what >>>>> contrast >>>>> matrix should I use? Normally I would use [0 0 1 -1] but this will >>>>> give >>>>> me >>>>> the significant differences in the age slopes not the mean values, >>>>> unless >>>>> I am missing something here. >>>> Correct, that will give you the difference in age/thickness slopes. >>>> You >>>> could do [1 -1 0 0] to give you the difference in intercepts. A better >>>> way, is to first look for differences in the slopes. If you do not >>>> find >>>> any, then rerun with DOSS with a contrast of [1 -1 0]. By using a >>>> DOSS, >>>> the difference in intercept is always constant regardless of age (as >>>> opposed to DODS). >>>> doug >>>>> Thanks in advance for your help and sorry for the lengthy message. >>>>> >>>>> Best, >>>>> Panos >>>>> _______________________________________________ >>>>> Freesurfer mailing list >>>>> Freesurfer@nmr.mgh.harvard.edu >>>>> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >>>>> >>>>> >>>> -- >>>> Douglas N. Greve, Ph.D. >>>> MGH-NMR Center >>>> gr...@nmr.mgh.harvard.edu >>>> Phone Number: 617-724-2358 >>>> Fax: 617-726-7422 >>>> >>>> Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting >>>> FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 >>>> www.nmr.mgh.harvard.edu/facility/filedrop/index.html >>>> Outgoing: >>>> ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ >>>> >>>> _______________________________________________ >>>> Freesurfer mailing list >>>> Freesurfer@nmr.mgh.harvard.edu >>>> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >>>> >>>> >>>> >>> _______________________________________________ >>> Freesurfer mailing list >>> Freesurfer@nmr.mgh.harvard.edu >>> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >>> >>> >> >> -- >> Douglas N. Greve, Ph.D. >> MGH-NMR Center >> gr...@nmr.mgh.harvard.edu >> Phone Number: 617-724-2358 >> Fax: 617-726-7422 >> >> Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting >> FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 >> www.nmr.mgh.harvard.edu/facility/filedrop/index.html >> Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ >> >> _______________________________________________ >> Freesurfer mailing list >> Freesurfer@nmr.mgh.harvard.edu >> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >> >> >> > > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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 . 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