On 10/29/2013 01:10 PM, Ashley Shurick wrote: > Hi all, > > I'm running analyses in Qdec and want to verify a few things: > > 1. When comparing two groups (HC vs patients) I am including mean > cortical thickness as a covariate, using the following equation: > > > bh.thickness = (lh.thickness*lh.surfarea + rh.thickness*rh.surfarea) / > (lh.surfarea + rh.surfarea) > > > Is this the best way to calculate global mean thickness? Yes > > > 2. I want to regress out any effects of age, therefore I need to > demean the ages for my groups as a whole, and not perform this > calculation on each group separately, correct? Yes, in which case the test of the difference between groups will be done at an age equal to the mean of the ages. > > 3. I'm including questionnaires as a covariate of interest - do I need > to demean these values as well? When you do a test on a continuous covariate, that test will be unaffected by demeaning of the covariate. Demeaning will affect the difference between groups if you use a separate covariate for each group. If you have a single covariate across groups, demeaning will have no effect.
doug > > > Thank you in advance for your help! > > > Ashley > > > -- > Ashley A. Shurick > Ph.D. Candidate > Department of Psychology > Stanford University > > > _______________________________________________ > 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 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.
