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Hi Donald and all, I have not used flexible factorial design before so I would like to ask very basic questions. How should I use it ? So firstly, can I use it instead of the paired t test? To repeat the the conditions : I have 8 subjects. Each subject scanned twice using right and left. Each scan has three conditions : A, B, & C. So I have A1,B1, & C1 using Right and A2, B2, & C2 using Left. So basically, I am struggling what I should input. So when I open Flexible factorial designin SPM8 I have these options: I have : - Factors - Specify Subjects or all scans & Factors - Main effects & interactions - Covariates Should I input in the field ( Specify Subjects or all scans & Factors) the con images subject by subject? How about the con images using right and left ? Then what should I input in the main effects & interactions? Thanks Aser On Wed, Oct 2, 2013 at 3:45 AM, MCLAREN, Donald <[log in to unmask]>wrote: > On Tue, Oct 1, 2013 at 4:14 PM, fMRI <[log in to unmask]> wrote: > >> Hi all, >> >> I am confused about which test or model I should select. >> >> I have scanned 8 subjects. Each subject was scanned in two sessions, left >> and right hand. Each session consists of three conditions: A, B & C. So >> basically I have from each subject six conditions using both hands. >> >> In the first level, i defined each condition in a separate regressor. >> Then I contrast each condition versus rest. So I have in each session : >> A>rest, B>rest, C>rest. >> >> So I end up by three contrast images per session or six per the two >> sessions. >> >> I am interested in comparing right versus left. So I would like to >> compare first A from session 1 versus A from session 2 and so on. >> >> I thought first to use two sample t-tests by taking the con from each >> subject in session 1 and condition A and compare that to session 2. And >> then do the same for Conditions B & C. >> >> Is this the right way to do it? >> > > No. You only have one sample. To compare two conditions from the same > subjects you need to use a paired t-test or create difference images for > the two sessions and use a one-sample T-test. The results will be the same. > > >> >> Or are there better options such as ANOVA? Can anyone please explain what >> should I select an how I should do this ? >> > > Flexible factorial (see my previous posts) can be used to compare 2 or > more conditions. This is basically a repeated measures ANOVA. > > >> >> Another consideration that it might be of interest is that I may need >> then to compare A1 versus B2 or C2 or B2+C2. >> > > I'm not quite sure why you would want to compare condition A from the left > hand to Conditions B and C with the right hand. Nevertheless, for A1 vs B2 > or C2, its paired t-test as above. If you want A1 vs B2+C2, I'd would > advise you to compare A1 to B2+C2 instead as two conditions will usually be > higher than 1. For A1 vs (B2+C2)/2 [which doesn't make sense due to > different hands], you'd create a contrast image for (B2+C2)/2 then use a > paired t-test. You could also use a flexible factorial with the contrast of > 1 -1/2 -1/2 as well. > > >> >> I believe if I do want to answer this question I cannot do two sample t >> test. So what would be the better approach? >> >> Thanks in advance! >> >> >> Aser >> > >