If there is no interaction between F/R and Active, then there should not be any theoretical difference between the two analyses, except that FR combined will be slightly more powerful since it has one more degree of freedom. You should first use the uncombined model to look for an interaction, and then proceed with the combined if there is no significant interaction.
There are several other things that could also come into play. First, it looks like the Rs have a much higher active score than Fs. This will create some correlation in the uncombined model and weaken the power. Second, it looks like there might be more Sex=1 in the R group; this will also weaken the uncombined model.
One more thing: you are not modeling sex properly. You should create four Classes (F-Male, F-Female, R-Male, and R-Female)
On 8/19/2019 8:32 AM, tange_neuro wrote:
External Email - Use Caution Hi all, I am deeply confused and terribly needed some help, and I failed to find the answer in the Freesurfer website. I had two patient groups F and R. To analysis the correlation between active time and cortical thickness, I tried two different methods A and B (A, treating patients in different group F and R as shown in attached figure A; B, treating all patients as one group FR as shown in attached figure B), and got distinctly different results. So, my questions: 1、Which one is actually correct for calculating the correlation between active time and thickness, and what does the other one mean? 2、Does "--cache 3 abs --cwp 0.999" means that the result is only corrected with vertex level P < 0.001, and no cluster level correction is conducted? I am looking forward to getting your help. Sincerely yours, Ge Tan
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