Dear experts, I’m observing – what I think – are implausible results from a simple correlational analysis between FA maps and body mass index, and was hoping if someone could shed some insight into what I’m doing wrong. Briefly: I have two groups of subjects, patients vs. controls (n = 21 in each group). I ran the entire preprocessing + TBSS pipeline as recommended. I then ran an unpaired t-test comparison of FA maps (while controlling for body mass index, age, and head motion) . This showed no significant between-group differences using randomize (TFCE, p < .05 corrected). As secondary analyses, I wanted to perform exploratory correlational analyses between FA maps and body mass index (within each group separately). I separated the all_FA_skeletonised 4D file into 2 separate 4D files, one for patients and one for controls. Then I generated a GLM for each group separately, with 3 regressors: body mass index, age, and head motion (the two latter are covariates of no interest). No demeaning was performed. I created the following t-contrasts: 1 0 0 and -1 0 0. This should give me the positive and negative correlations between FA maps and body mass index, while controlling for age and head motion. I then ran: randomise –i FA_Patients_skeletonised –o BMI –m mean_FA_skeleton_mask –d BMI.mat –t BMI.con –n 5000 –T2 –uncorrp -V I did this for the controls as well, using their FA maps. When looking at the BMI_tfce_corrp_tstat1 files (positive correlations) for each of the two groups, with a threshold of min 0.95 and max 1, there are significant results throughout all WM fibers. Indeed, the images look more like a WM skeleton file, and not a result image (see attachment). This is the case for both the patient and the control group. This is NOT the case for the BMI_tfce_corrp_tstat2 files though, which showed no results. I also performed similar correlational analyses using the same input files and basic GLM design, but with another regressor of interest (a self-report measure). This analysis showed no significant correlations. See attachments for my design and results (thresholded at p < .05 corrected using tbss_fill). Am I doing something wrong here; and why do these “implausible” results occur only with positive correlations between BMI and FA maps? All help is highly appreciated! Best, -Lasse Lasse Bang, Ph.D Postdoctoral Researcher Regional Department for Eating Disorders (RASP) Oslo University Hospital, Ullevål HF Oslo, Norway E-mail: [log in to unmask]<mailto:[log in to unmask]> / [log in to unmask]<mailto:[log in to unmask]> Phone: +47 23 02 73 71 /+47 41 42 97 04 IKKE SENSITIVT INNHOLD [cid:8238B72BDFCBF843A67F580535EBB492@ous-hf.no] [cid:2D244123BC038A42AAB205104A839C89@ous-hf.no] [cid:F54830810FDB694D88E6BAE59C41E697@ous-hf.no]