Dear Doug, I don't understand what you mean by " the variance of the fMRI time series". I fed Freesurfer only structural MRI data. Does that mean that Freesurfer automatically assumes the data to be longitudinal? I really hope not.
Sincerely, Ye On Tue, Apr 14, 2015 at 8:11 PM, Douglas Greve <gr...@nmr.mgh.harvard.edu> wrote: > In theory, WLS is the optimal estimator in the case where variance > differs across subject. The FS implementation actually computes > "psuedo-WLS" in which the weights are just the inverse of the first level > variance. A true WLS would use the random effect variance plus the lower > level variance. The first level variance is determined from the variance > of the fMRI time series. > > doug > > > On 4/13/15 6:42 PM, ye tian wrote: > > Hello Freesurfers, > > I would like to be a little more specific about my question. Was > heteroskedasticity a reason for Weighted Least Square (WLS)? If so, how did > Freesurfer determine the weights? > > Thank you! > > Sincerely, > Ye > > > > > On Mon, Apr 13, 2015 at 4:59 PM, ye tian <tianye...@gmail.com> wrote: > >> Dear Freesurfers, >> >> Can someone please explain to me why WLS was chosen as the method of >> regression? >> >> Thank you very much! >> >> Sincerely, >> Ye >> > > > > _______________________________________________ > Freesurfer mailing > listfreesur...@nmr.mgh.harvard.eduhttps://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. > >
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