Hi Lihong,

I think the F(2,14) instead of T(15) is arising from having selected possibly a between-conditions contrast of [1 0; 0 1] instead of [-1 1]. That would be looking at any differences between the two groups either pre or post intervention, instead of looking at a group-by-intervention interaction. Can you please double-check?

Best

Alfonso

Originally posted by Lihong Wang:

Thank you so much Alfonso for your prompt response. I attached the snapshot.

I guess you are right, in the model figure, it did say F(2,14), but as you can see from the overlayed image, it indicated F(2,30). Also, why the first df is 2 instead of 1?

Thank you.

--Lihong

Originally posted by Alfonso Nieto-Castanon:

Dear Lihong

That is strange indeed, with 20 subjects a second-level of the form: 

Subject effects: GroupA, GroupB, ControlVariable1, ControlVariable2, ControlVariable3

Between-subjects contrast: [1 -1 0 0 0]

Conditions: Pre, Post

Between-conditions contrast: [-1 1]

would typically result in statistics of the form T(15) for a SBC (seed-based connectivity) analysis in CONN, so I am not totally sure what the F(2,30) indicates. Could you please send me a screenshot of where exactly the F(2,30) stats are shown so I can better understand what they represent? (see in the example images attached the typical places where you would see reported the stats associated with SBC group-level analyses, and where I would expect to see the "T(15)" indication for your analysis)

Hope this helps

Alfonso

Originally posted by Lihong Wang:

Dear Alfonso,

I 've posted a question regarding the  2 groups with 2-within subjects (pre, post intervention) model we used. We 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? The results indicate a significant functional connectivity between seed mPFC and inslua with F(2,30)=8.xxx in Conn results page. The reviewer questioned the first df and pointed out that it should be 1 (2-1)*(2-1)=1 instead of 2. The reviewer also questioned the calculation of the second df =30 with n=20. It seems that with n=20, df should be 20*2(pre, post) - 3covariates*2=34. Is it possible that Conn also regressed out other covariates that we aren't aware of? Any thoughts? Thank you.

 

--Lihong