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.
- 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.
- 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