Hi Jose, with 6 classes and 3 continuous variables, I think you should have 24 regressors, which means 24 columns in the contrast matrix. Yours only has 18. Otherwise the contrast to test between B and C is correct (just need to add 6 zeros). For the interaction, you would need
0 0 0.5 -0.5 -0.5 0.5 0 0 .... doug Jose Luis Cantero Lorente wrote: > > Dear Freesurfers, > > > > My experimental design includes 2 discrete factors and 3 continuous > variables: > > > > Discrete factors: > > - Diagnosis with three levels (A, B, C) > > - Gender with two levels (Males, Females) > > > > Continuous variables: > > - Mean cortical thickness in the left hemisphere (CTLH) > > - Age > > - Performance in a memory test (TASK) > > > > The FSGD file would be as follows: > > > > GroupDescriptorFile 1 > > Title Thickness-subj > > Class AMale > > Class AFemale > > Class BMale > > Class BFemale > > Class CMale > > Class CFemale > > variables ZCTLH ZAGE > > Input control_01 AMale -1.04398 0.24789 > > Input control_02 AMale 1.22853 -0.72343 > > Input control_03 AFemale .13773 -1.37097 > > Input control_04 AFemale .41043 0.24789 > > Input mci_01 BMale -.77128 0.24789 > > Input mci_02 BMale -2.40749 0.73354 > > Input mci_03 BFemale -.86218 -1.0472 > > Input mci_04 BFemale .50133 0.23777 > > Input ad_01 CMale -.75678 0.22789 > > Input ad_02 CMale -2.88749 0.63047 > > Input ad_03 CFemale -.96015 -1.4452 > > Input ad_04 CFemale .80712 -0.37567 … > > > > We are assuming different offsets and different slopes (DDOS). > > > > The following contrast would test the null hypothesis whether there is > a difference between B and C (T-test) regressing out the effect of the > remaining variables. > > > > 0 0 0.5 0.5 -0.5 -0.5 0 0 0 0 0 0 0 0 0 0 0 0 > > > > Could you help me to build the contrast for testing interactions in > the above experimental design? In the FSwiki examples, you add one > column when you have two factors with two levels each, and one > continuous variable. I am not sure how many columns should I add in > our particular case and why. > > > > Null hypothesis: is there an interaction between diagnosis (B > C) and > gender regressing out the two remaining variables? Assuming that you > add one column per variable that is regressed out, the contrast would > be as follows: > > > > 0 0 0.5 0.5 -0.5 -0.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 > > > > Is this correct? Any help will be very appreciated. > > > > Many thanks in advance. > > > > Best regards, > > Jose > > > --- > Jose L. Cantero, Ph.D. > Laboratory of Functional Neuroscience > Department of Physiology, Anatomy and Cell Biology > University Pablo de Olavide > Ctra. de Utrera, Km.1 > 41013 - Seville > - Spain - > Phone: +34 954 977433 > Fax: +34 954 349151 > Email: jlcan...@upo.es > http://www.upo.es/neuroaging/en/ > ------------------------------------------------------------------------ > > _______________________________________________ > 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.
