You can get the SSE from rvar*DOF (eg, fscalc rvar.mgh mul 100 -o sse.mgh). You can get the SST using fscalc y.mgh sqr -o sst.mgh mri_concat sst.mgh --sum --o sst.mgh Then the unadjusted r-squared as fscalc sse.mgh div sst.mgh sub 1 mul -1 -o rsquared.mgh The final calculation is a little obtuse but it realizes r2 = 1 - sse/sst
For judging the model, you can compare the rvars. I think you can also test the significance of the regressor you added. doug On 01/06/2016 01:00 PM, Peggy Skelly wrote: > Hello Freesurfer statistical experts, > > I need some assistance in explaining the output generated by > mri_glmfit (then followed by correction for multiple > comparisions, mri_glmfit-sim). We fit one model and got some > statistically significant clusters. Then, we ran another model, the > same plus an additional nuisance variable. It had similar significant > clusters. How do we compare the results from the 2 different models? > Which model is better? > > In other statistic programs, we could examine an R^2 value, which can > be interpreted as the percent of the response variable variation that > is explained by the model. The model with the higher R^2 would be > considered better since it fits the data better. But the output from > mri_glmfit has rvar.mgh - the sum of the squares of the residual > error divided by the DOF. So it would seem that a lower rvar would > indicate a better fit. Can rvar.mgh be used to compute an R^2, because > the R^2 concept is more widely understood. Or, is there a way to > explain rvar in lay terms similar to R^2? > > Thanks, > Peggy > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
