Hi Jenessa, Jenessa Price wrote: > I'm examining differences in cortical thickness in a sample of drug > users and non-users. From the literature, it appears that the 2 > covariates I should use for the GLM analysis will be gender and age. > Other researchers have examined other possible covariates (like age of > first use, # past year uses, IQ, etc.) using correlations between > those variables and significant clusters that differed between > groups. Is this the best way to go about translating a typical > regression model into the Freesurfer statistical package (especially > if I'm interested in dose-dependent relationships)? The age, gender, and eTIV (estimated Total Intracranial Volume) are typically used as nuisance variables. If age of first use, etc, are dose-dependent and you're interested in a dose relationship, then I would include one. You can also include more than one and use an F-test. > > Also, how do you suggest controlling for total brain volume? Other > researchers have performed univariate analyses between groups on TBV > controlling for age and gender, then examined mean cortical thickness, > but I'm not quite sure what the steps are for this. Could someone > help me identify the best way to control for TBV (i.e., is there a way > to control from the first GLM analysis, or is this a possible > covariate to enter in to the analysis)? Gender is a good way to control for TBV, since that is the biggest effect. You can also use the eTIV mentioned above to correct for head size. Note that this is a difference between head size and brain size as brain size can shrink with age (and maybe drug use?).
doug > > Thanks! > > -- > Jenessa S. Price, M.A. > Graduate Student, Clinical Psychology and Neuropsychology > University of Cincinnati > Campus Representative, American Psychological Association of Graduate > Students (APAGS) > > ------------------------------------------------------------------------ > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center [email protected] Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html _______________________________________________ Freesurfer mailing list [email protected] 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.
