yes, that is correct Gabriel Go.Es. wrote: > Dear Doug, > > I really appreciate all your answers, and to be sure that I understood > the reasoning for setting the contrast for the interaction effect. > > Let's assume that we have 9 groups (two factor, with three levels each). > > G1-left > G1-right > G1-ambi > G2-left > G2-right > G2-ambi > G3-left > G3-right > G3-ambi > > [1 -1 0 -1 1 0 0 0 0]/2 > [1 0 -1 -1 0 1 0 0 0]/2 > [1 -1 0 0 0 0 -1 1 0]/2 > [1 0 -1 0 0 0 -1 0 1]/2 > > However, if we have 8 groups (two factors, one of them with 4 levels) > > G1-male > G1-female > G2-male > G2-female > G3-male > G3-female > G4-male > G4-female > > [1 -1 -1 1 0 0 0 0]/2 > [1 -1 0 0 -1 1 0 0]/2 > [1 -1 0 0 0 0 -1 1]/2 > > Is this correct? > > Thank you very much in advance, > Gabriel > > > > > > > > ------------------------------------------------------------------------ > Date: Wed, 9 Mar 2011 22:22:18 -0500 > From: gr...@nmr.mgh.harvard.edu > To: gabriel...@hotmail.com; freesurfer@nmr.mgh.harvard.edu > Subject: Re: [Freesurfer] glm question > > > two row contrast matrix > > [1 1 -1 -1 0 0] > [1 1 0 0 -1 -1]/2 > > 1st row test for a difference bet G1 and G2 > 2nd row tests for a difference bet G1 and G3 > Note that you don't need to test G2 vs G3 (that is implied by the > other two tests). > > doug > > > On 3/9/11 7:33 PM, Gabriel Go.Es. wrote: > > > Thanks a lot, > just one another question Doug, > how to set an ANOVA for group differences??' > > Gabriel > > > > > > > Date: Wed, 9 Mar 2011 17:52:03 -0500 > > From: gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > > To: gabriel...@hotmail.com <mailto:gabriel...@hotmail.com>; > freesurfer@nmr.mgh.harvard.edu <mailto:freesurfer@nmr.mgh.harvard.edu> > > Subject: Re: [Freesurfer] glm question > > > > > > > > Gabriel Go.Es. wrote: > > > > > > Thank you so much, Doug > > > > > > I've check at your update and saw that this contrast has to be > /2, > > > wich I guess means 0.5 instead of one to keep the scale right? > > Yes. > > > > > > and the contrast for me, would be something like: > > > Let's suppose > > > group1_males > > > group1_females > > > group2_males > > > group2_females > > > group3_males > > > group3_females > > > for differences between males and females (males > females) > > > regreessing the efects of group would be: > > > [0.333 -0.333 0.333 -0.333 0.333 -0.333] > > Correct > > > differences between group1 & group 3 regressing the effects of > gender: > > > [0.5 0.5 0 0 -0.5 -0.5] > > Correct > > > and the differences between males and females for a single > group can be: > > > [1 -1 0 0 0 0] > > > am I right??? > > Yes > > > but I don't yet figure out how to set a difference from 0 in > any of > > > the group means (to meassure the effect of group), nor the > interaction > > > between group and gender, and that's because my model is not > like the > > > one from the example, > > Try using > > [1 -1 -1 1 0 0] > > [1 0 0 0 -1 1] > > > > This is a single matrix with two rows. The first row tests for an > > interaction between G1/2 and M/F. The second row tests for G1/3 > and M/F. > > Note that you don't need a third row. > > > > > > > > > > > > > > > > > > > > > Date: Wed, 9 Mar 2011 14:52:37 -0500 > > > > From: gr...@nmr.mgh.harvard.edu > <mailto:gr...@nmr.mgh.harvard.edu> > > > > To: gabriel...@hotmail.com <mailto:gabriel...@hotmail.com> > > > > CC: freesurfer@nmr.mgh.harvard.edu > <mailto:freesurfer@nmr.mgh.harvard.edu> > > > > Subject: Re: [Freesurfer] glm question > > > > > > > > That contrast is wrong. I've updated this page with the > correct contrast > > > > https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf6G0V > > > > which is: > > > > > > > > |+1 -1 0 -1 +1 0| > > > > |+1 0 -1 -1 0 +1| > > > > > > > > This is an F-contrast (two rows). The first row looks for a > difference > > > > between L and R for M and F (ie, a simple interaction > between LR and > > > > MF). The second row looks for a difference between L and A > for M and F. > > > > If either of these subcontrasts shows an effect, then there > is an > > > > interaction. > > > > > > > > doug > > > > > > > > > > > > Gabriel Go.Es. wrote: > > > > > > > > > > Dear FreeSurfer experts, > > > > > > > > > > > > > > > > > > > > I'm doing some group analyses and I'm a little stocked > with this: > > > > > > > > > > I have Six Groups (2 Factors, one with three levels and > the other one > > > > > with two levels), and one covariate. I don't know the rule > for > > > setting > > > > > the contrasts for an ANOVA and for the interaction between > the two > > > > > factors regressing out the covariate. I've checked at the > FS wiki and > > > > > found the following contrast for six groups (two factors) > and zero > > > > > covariates. > > > > > > > > > > > > > > > > > > > > Contrast 6 gender-x-handedness.mtx (interaction between > gender and > > > > > handedness) > > > > > > > > > > [0.333 -0.333 -0.333 0.333 0.000 0.000 0.000 0.000 0.000] > > > > > > > > > > [0.000 0.000 0.000 0.000 0.000 0.333 -0.333 -0.333 0.333] > > > > > > > > > > > > > > > > > > > > I don’t understand the rule that has been followed. > > > > > > > > > > Can any one help me with this? > > > > > > > > > > > > > > > > > > > > Bests, > > > > > > > > > > Gabriel > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > > > _______________________________________________ > > > > > 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: > www.nmr.mgh.harvard.edu/facility/filedrop/index.html > <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> > > > > > > > > > > > > > > > > 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 <mailto: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 > <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> > > >
-- 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
