Yes, I agree completely. We are using DODS and it is clear that we have different results depending on which type of ICV we use. The question is... which type of ICV correction for DODS is the most statistically sound? demean across all groups, no demeaning, or demean within groups separately.
What would you recommend. On Mon, Aug 29, 2016 at 3:33 PM, Douglas N Greve <gr...@nmr.mgh.harvard.edu> wrote: > If there was not an interaction between group and ICV, I would say to > use DOSS where demeaning does not make a difference. Since there is an > interaction, you have to use DODS, but the interpretation is no longer > easy. If you do not demean, then you are implictly testing for a > difference at ICV=0 (this is what "regressing out" means). If you > demean, you are implicitly testing at ICV=MeanICV. The problem is that > the results can change depending on the ICV you test it at. > > > On 08/29/2016 02:53 PM, Corinna Bauer wrote: > > Sorry for not specifying. Yes, we are looking at difference in volume > > between the two groups using DODS. What is the most statistically > > sound... raw values, demeaning across the entire sample, or demeaning > > with groups separately? FYI, I exported the ICV values to SAS and > > there is a significant different between the two groups for ICV. > > > > > > > > On Mon, Aug 29, 2016 at 2:48 PM, Douglas N Greve > > <gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>> wrote: > > > > not sure what you are testing, but if you are, eg, looking at the > > difference between two groups regressing out ICV, then it can make a > > huge difference > > > > > > On 08/29/2016 12:36 PM, Corinna Bauer wrote: > > > Hello all, > > > > > > I am wondering why results would change completely for between > group > > > volume analysis when using demeaned/mean-centered ICV compared to > > > using ICV as a covariate in mri_glmfit? See the figures below. > > > > > > Does demeaning the covariate inherently change the results > > comapred to > > > the raw covariate values? > > > > > > Thanks > > > > > > Corinna > > > > > > > > > _______________________________________________ > > > Freesurfer mailing list > > > Freesurfer@nmr.mgh.harvard.edu > > <mailto:Freesurfer@nmr.mgh.harvard.edu> > > > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > <https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer> > > > > -- > > Douglas N. Greve, Ph.D. > > MGH-NMR Center > > gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > > Phone Number: 617-724-2358 <tel:617-724-2358> > > Fax: 617-726-7422 <tel:617-726-7422> > > > > Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting > > <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > > FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 > > <https://gate.nmr.mgh.harvard.edu/filedrop2> > > www.nmr.mgh.harvard.edu/facility/filedrop/index.html > > <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> > > Outgoing: > > ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ > > <ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/> > > > > _______________________________________________ > > Freesurfer mailing list > > Freesurfer@nmr.mgh.harvard.edu <mailto:freesur...@nmr.mgh. > harvard.edu> > > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > <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 > > <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. > > > > > > > > > > _______________________________________________ > > 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 >
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