I don't want to speak for the Freesurfer team, but I am 99% certain that it is Direct/Standard as you list them. There isn't any stepwise variable selection going on.
________________________________________ From: freesurfer-boun...@nmr.mgh.harvard.edu [freesurfer-boun...@nmr.mgh.harvard.edu] on behalf of L. Schweren [l.j.s.schwe...@umcg.nl] Sent: Tuesday, March 25, 2014 6:08 AM To: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] glmfit with correlated covariates Dear FreeSurfer experts, Thank you for your fast reply. We are extracting cortical thickness values for statistical sub-analyses in SPSS (due to corrections required with regard to family relatedness within the data); therefore we want to be a 100% certain that the statistical model we use in SPSS is identical to the model used by mri_glmfit. Can you confirm that, out of the multiple linear regression types listed below, mri_glmfit makes use of the Direct (or Standard) regression model? Type Characteristics Direct (or Standard) · All IVs are entered simultaneously Hierarchical · IVs are entered in steps, i.e., some before others · Interpret: R2 change, F change Forward · The software enters IVs one by one until there are no more significant IVs to be entered Backward · The software removes IVs one to one until there are no more non-significant IVs to removed Stepwise · A combination of Forward and Backward MLR Thank you again for your help, Best wishes, Lizanne Date: Wed, 12 Mar 2014 11:04:00 -0400 From: Douglas Greve <gr...@nmr.mgh.harvard.edu> Subject: Re: [Freesurfer] glmfit with correlated covariates To: freesurfer@nmr.mgh.harvard.edu Message-ID: <53207760.8010...@nmr.mgh.harvard.edu> Content-Type: text/plain; charset="iso-8859-1" It is just a standard multiple regression analysis where all regressors are fit simultaneously. One weight does not include that of another weight. doug On 3/12/14 5:16 AM, L. Schweren wrote: > > Dear FreeSurfer experts, > > I am attempting to disentangle the effects of different features of > pharmacological treatment on cortical thickness. > > I am running glmfit from the commandline, with multiple covariates > (a.o. Z_Age, Z_TreatmentDuration and Z_StartAge) in the fsgd-file. > These covariates are correlated up to approximately 0.6 , which to my > understanding is not ideal yet not inducing collinearity. Running > glmfit, I do not get any errors such as ill-designed matrix or so. > > My question regards the way the different regression weights are > calculated in each voxel. If I test the variance in CT of voxel A > explained by for example TreatmentDuration, and part of the variance > in voxel A is explained by both TreatmentDuration and StartAge, will > the regression weigth of TreatmentDuration than include the part that > is also explained by StartAge? Or are all other covariates first > "regressed out" of the variance, such that the variable I test can > only explain the variance that was not explained by any of the other > covariates? > > Thank you very much, your help is very much appreciated! > > Best wishes, > > Lizanne > > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer _______________________________________________ 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.