krista kelly wrote: > Hi, just wondering if anyone has any advice on the following questions: > > I'm using QDEC to analyze cortical thickness differences between > groups and I have a few questions: > > 1) There are a few variables that I need to control for. First > variable is scanner - I used two different scanners of different field > strengths (1.5T GE and 3T Siemens) so I wanted to control for scanner. > I also wanted to control for age and gender. Here's my ideal design > setup: > > discrete variables - groups, scanner, gender > nuisance variable - age > > contrast would be 1 -1 0 0 0 0 > > I realize that scanner, gender, and group are all discrete variables, > and that age would be a continuous one. However, in the design tab, I > am not able to select all 3 discrete variables (groups, scanner, and > gender). Should I designate scanner or gender as a nuisance variable > instead? Would it matter which one I use as the nuisance variable? > Possible setup: > > discrete vars - groups, scanner > nuisance vars - age, gender > > contrast - 1 -1 0 0 (Correct?) Unfortunately, you cannot use QDEC if you have three groups. You'll have to create an FSGD file and contrasts by hand, then run mri_glmfit. Do a search for FSGD on our wiki and go to the examples page. I think there is an example there for what you want to do. > > 2) If I use DODS, should I demean the ages if age is a nuisance variable? You should actually test whether there is an interaction between age and your group contrast of interest (using the DODS model). If there is not interaction, then switch to a DOSS where demeaning does not matter. > > 3) If I use a smoothing kernel during the analysis, then create an ROI > and map that ROI to each individual subject, will the resulting .stats > file in each subjects stats folder reflect the smoothed data or does > mapping onto each ROI just extract the raw unsmoothed data from each > vertex? It depends on how you do the extraction. If you are using mris_anatomical_stats on each individual's unsmoothed data, then it will reflect the unsmoothed.
doug > > Thanks! > Krista > ------------------------------------------------------------------------ > > _______________________________________________ > 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: www.nmr.mgh.harvard.edu/facility/filedrop/index.html _______________________________________________ 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.
