On 04/25/2016 05:28 AM, Jockwitz, Christiane wrote: > > Dear FreeSurfer Experts, > > I’ve got a question regarding effect sizes: I did a local gyrification > analysis using QDEC. I obtained several significant clusters from the > analysis for whom I would like to calculate some effect sizes. > > On the website/helpline, I saw that fscalc might do this job. > Therefore, I would need the gamma.mgh file as well as the rstd.mgh file > > 1.The gamma.mgh is supposed to contain the contrast effect size. What > coefficient of determination is that? > Not sure what you mean. The gamma.mgh is just the value of the contrast which is gamma = C*beta, where beta are the regression coefficients, so gamma is a type of regression coeff > > 2.When the gamma.mgh is divided by the standard deviation (rstd.mgh), > I get an output.mgh file, which contains positive as well as negative > values ranging from -1 to +1. Since I don’t know which coefficient of > determination is used in this calculation, I have problem to interpret > these values. What value would be a high/low effect size? > Further from zero (pos or neg) would be larger. > > 3.I would like to calculate this effect size for my significant > cluster instead of vertex-wise effect size. I tried to perform this > using mri_segstats. Is that right? > Yes, you can do that. What will you do with the result? The final effect size value is not meaningful because it is a circular computation (ie, it is going to be an overestimate because you have selected voxels that had a high effect size to begin with). > > Thank you very much in advance. > > Best > > Christiane > > > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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