Dear FSL experts, I am very interested in knowing the answer to this question. I would highly appreciate your help in this issue. Kind regards, Rosalia. ---------- Forwarded message ---------- From: Paul Macey <[log in to unmask]> Date: 2015-10-20 18:00 GMT+02:00 Subject: [FSL] FIRST beta values To: [log in to unmask] I'm running a 4-variable analysis in FIRST (one group, three covariates), and I have significant results with the F-test. I now want to see the direction and size of the effects; in a typical model I would look at the betas/model coefficients, but these are not available with the vertex analysis. I see in the documentation ( http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIRST/UserGuide#randomise) the recommended approach is to do a t-test, or look at the actual values with the FSL timeseries tool (or by extracting the data). The problem with the t-test is that I only get one result ("....tstat1") even though I have 4 contrasts (see design.con below), and I get 4 F stats. I'm not sure which contrast tstat1 refers to, and furthermore I'm not sure how to translate the t statistic for this 4-variable model to an effect size. For a t statistic from a 2-sample t test multiplying by std/sqrt(N) would work - is it the same with a 4 variable model? Similarly, the issue with extracting the individual values is that I while I could look for group differences, I cannot account for the 3 other variables in the model without running another analysis on the extract values, which is possible but no ideal. So my questions are: - is it possible to obtain the betas? if no, - how can I obtain the t statistic maps for my 4 contrasts? - is there a way to translate the t statistic in this 4-variable model to a non-standardized effect size? Any guidance appreciated! ------------------- design.con /ContrastName1 group mean /ContrastName2 TIVvol mean /ContrastName3 age mean /ContrastName4 sex mean /NumWaves 4 /NumContrasts 4 /PPheights 1.552420e+00 1.719039e+00 9.529518e+01 1.722726e+00 /RequiredEffect 0.673 0.673 0.560 0.417 /Matrix 1.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e+00