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