We have two groups with total n=20, each subject had pre and post MRI scans. I controled for age, sex, and mean headmotion. I modeled [1 -1 0 0 0] for betwee-subjects, and [1 -1] for within-subjects contrasts. With this model, I got F(2,30)>8.64 for significant functional connectivity pair with seed-to-voxel analysis. The review questioned why the group df was 2 not (2-1)*(2-1)=1, and why the subjects df=30?

Lihong

Originally posted by Lihong Wang:

I have a quick follow-up question: For 2 groups with 2-within subjects (pre, post intervention) model, I have three variables to be controlled. Is it correct to model [ 1 -1 0 0 0] for between-subjects and [1 -1] within-subjects contrast?

Thank you,

Lihong

Originally posted by Alfonso Nieto-Castanon:

Hi Emanuele, For a 2x2 group*condition interaction, simply select both groups in the 'subject effects' list and both conditions in the 'conditions' list, and then enter [1 -1] in both the 'between-conditions contrast' field as well as in the 'between-subjects contrasts' field. This is going to look at whether the difference between conditionI and conditionII is larger in groupI compared to groupII (take the two-sided results instead, if you do not have an a priori hypothesis about the directionality of this interaction) Best Alfonso Originally posted by Emanuele Pravata':

Hi again, I understand that the following: "'between-condition' contrast of [1 -1 0; 0 1 -1] and select all three groups and enter a 'between-subjects' contrast of [1 -1 0; 0 1 -1]" will detect any interaction group*condtion, a 3x3 ANOVA. I would like to do the same with 2 groups and 2 conditions (temporal points): should I enter the following contrasts: [1 -1; -1 1] or [1 0; 0 1] or any other? Thank you again! E