Charlotte, There is no difference, from a statistical perspective, of nuisance factors and covariates.
The key questions are: (1) Do any of these covariates have a differential effect on thickness between groups? (2) Do you want to compare the actual group means or the covariate-adjusted group means (e.g. test the means for subjects as if the subjects all had the same covariate values)? (3) Do you have enough subjects to add 5 covariates? (4) Do you have a valid reason for why all the covariates would have an effect on thickness? One can always add more covariates to reduce the error, but its not always a good thing to add covariates just to reduce the error of the model. On 2/23/12, Charlotte Bernard <chak...@live.fr> wrote: > > Dear Freesurfur users, > > I have a question about the design for a surface based analysis! I want to > compare controls and patients. I have 5 covariates. One is a continous > variable. The others are categorial variables (4 with 2 levels and 1 with 5 > levels). I want to ajust my result with all of thoses variables. I am > interested in the difference in thickness between patients and controls. > Is it possible to construct such design? > Can I put some of my variables in the "nuisance factors" ? I don't really > understand the difference between "nuisance factor" and covariabes. > I really hope somebody can help me. > Thanks for all! > All the best, > Charlotte > -- Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Postdoctoral Research Fellow, GRECC, Bedford VA Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. _______________________________________________ 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.
