On 09/06/2012 04:42 AM, Meng Li wrote: > Hi Freesurfer experts, > When I perform the statistical analysis, I am very confused with the > following questions: > > My experimental design includes 3 discrete factors: diagnosis with two > levels (A, B); genotype with two levels (G, T); gender (F, M), and two > covariates. > > So I can get 8 classes: AGF, AGM, ATF,ATM, BGF, BGM, BTF, BTM. > > 1) I want to perform 2 (diagnosis)* 2(genotype) interaction analysis > with regressing out the effect of gender and two covariates, but I > don't know the rules for setting the contrasts for the interaction. > The contrast matrix I used is: > > 0.250.25 -0.25-0.25 -0.25 -0.25 0.25 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 > > is it correct? > > If it is correct, how to explain the results, for example, what does > the positive (or negative) clusters stand for? Or the clusters showed > in the t-test statistical map are the regions that have the > significant interaction? > This is correct. As with all interactions, the sign is hard to interpret. Most people will do post hoc analyses to help interpret the results. > > 2) When I perform the main effect of dignosis, is the following > matrix I used correct? > > 0.25 0.25 0.25 0.25 -0.25 -0.25 -0.25 -0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 > 0 0 0 (I think it regressed out the effect of genotype and gender, > that is it takes the genotype as a covariable) > > Or I should create another fsgd file, that has 4 classes: AF, AM, BF, > BM. And I can use the matrix (0.5 0.5 -0.5 -0.5 0 0 0 0 0 0 0 0) to > perform the main effect of diagnosis. which one is right? > Your contrast is correct. doug > > Any help will be very appreciated. > > Best wishes, > > Meng > > > > > > > > > > _______________________________________________ > 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.
