It will tend to weight smaller groups by a proportion greater than the number of subjects in the group.
On 02/18/2014 01:58 PM, Yang, Daniel wrote: > Thanks Doug! One follow-up question: since it's [0.25 0.25 0.25 > 0.25], would the effect be biased toward large sample sizes in one of > the groups (versus the other groups)? > > Or, does FreeSurfer qdec take care of the unequal cell, in a possible > way analogous to using Type III SS in the traditional ANOVA? > > Best, > Daniel > -- > Daniel (Yung-Jui) Yang, Ph.D. > Postdoctoral Researcher > Yale Child Study Center > New Haven, CT > Tel: (203) 737-5454 > E-mail: _yung-jui.yang@yale.edu_ > > On 2/18/14 1:30 PM, "Douglas N Greve" <gr...@nmr.mgh.harvard.edu > <mailto:gr...@nmr.mgh.harvard.edu>> wrote: > > That looks right to me > doug > > > On 02/18/2014 10:08 AM, Yang, Daniel wrote: > > Dear FreeSurfer experts, > > I have two binary factors (F1: F1L1 F1L2; F2: F2L1 F2L2), 1 > covariate > (COV), and 1 nuisance factor (NUI). I want to make sense of some > specification of the regressors and contrasts. > Because they are not described > in http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G1V, I post my > understanding below. Can you let me know if it is correct? > > This model using the DODS method will have 12 regressors: > > Regressor1: 1's for F1L1 F2L1, 0 otherwise (i.e., offset for > Group 1) > Regressor2: 1's for F1L1 F2L2, 0 otherwise (i.e, offset for > Group 2) > Regressor3: 1's for F1L2 F2L1, 0 otherwise (i.e., offset for > Group 3) > Regressor4: 1's for F1L2 F2L2, 0 otherwise (i.e., offset for > Group 4) > Regressor5: COV for Group1 subjects, 0 otherwise (i.e., COV > slope for > Group 1) > Regressor6: COV for Group2 subjects, 0 otherwise (i.e., COV > slope for > Group 2) > Regressor7: COV for Group3 subjects, 0 otherwise (i.e., COV > slope for > Group 3) > Regressor8: COV for Group4 subjects, 0 otherwise (i.e., COV > slope for > Group 4) > Regressor9: NUI for Group1 subjects, 0 otherwise (i.e., NUI > slope for > Group 1) > Regressor10: NUI for Group2 subjects, 0 otherwise (i.e., NUI > slope for > Group 2) > Regressor11: NUI for Group3 subjects, 0 otherwise (i.e., NUI > slope for > Group 3) > Regressor12: NUI for Group4 subjects, 0 otherwise (i.e., NUI > slope for > Group 4) > > Description1: Does the correlation between thickness and COV, > accounting for F1 and F2, differ from 0? Nuisance factors: NUI > Contrast1: [0 0 0 0 0.25 0.25 0.25 0.25 0 0 0 0] > > Best, > Daniel > > -- > Daniel (Yung-Jui) Yang, Ph.D. > Postdoctoral Researcher > Yale Child Study Center > New Haven, CT > Tel: (203) 737-5454 > E-mail: _yung-jui.yang@yale.edu_ <mailto:_yung-jui.yang@yale.edu_> > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > <mailto: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 <mailto: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 <mailto: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. > > -- 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
