On 07/16/2012 09:30 PM, Meng Li wrote: > Dear professor, > Thanks for your reply. > You said that when drawing conclusions from both hemispheres then I > need to use .025, but I found that in qdec interface, the default > value of -cwpvalue is 0.05. So are they inconsistent? This would be consistent for a single hemisphere, which is all that qdec analyzes. > I also want to find a solution about an ERROR. > I tried to run a cortical thickness analysis to look for differences > between two groups (patients and controls) with regressing out the > gender factor, the patients group have 1 female and 17 male, after > analysis, I got the results. But when I add another continuous > variable as covariate, I received the message: "ERROR: matrix is > ill-conditioned or badly scaled." Then I tried to change the gender > composition the patients groups: 2 female/16 male, and the problem was > solved. so is it right about what i did, or I need another way to > solve this problem? It is probably a bad idea to try to put a subject that is in one group into another group. In your case, you need more females. You can't have a single member in a group and have a covariate. You should try to have balanced groups. With only a single member of a group, you are going to have problems with power and be susceptible to that one member being an outlier.
doug > Thanks, > Best wishes > Meng > > On 07/06/2012 10:00 PM, Meng Li wrote: > > Hi, freesurfer expert, > > I performed the statistical analysis between two groups first in left > > hemisphere, and got some regions which showed different. > > 1) so if I then do multiple correction, i don't need to run the > > mri_glmfit-sim command, and just press the button of the monte carlo > > null-z simulation in the qdec interface, am i right? > correct > > 2) Whether mri_glmfit-sim --cache command line and the mc-z in qdec > > get the same results, or not? and as to the option --cwpvalthresh, > > should i choose 0.05 or 0.025? > If you are drawing conclusions from both hemispheres then you need to > use .025 > > 3) And what is the difference between fdr and mc-z correction? > mc-z uses a cluster-wise correction and controls the rate of false > positive clusters. FDR is voxel-wise and controls the false discovery > rate, which is the number of false positives relative to the total > number of positives (as compared to the number of false positives > relative to the total number of tests). > doug > > Thanks, > > > -- > > -- 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: www.nmr.mgh.harvard.edu/facility/filedrop/index.html _______________________________________________ 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.
