Hello Martin, thanks for the quick reply !
as I understood, from the "LongitudinalTutorial", after long_mris_slopes the results can be seen for each subject, and in order to see the group results, all subjects should be analysed in the Qdec, and there I could see the results for each group, but couldn't do the inter-group, this is why we tried the "RepeatedMeasuresAnova" Indeed, there is some difference in the time distance, so we will try your new idea ! I know about Jorge's work - Marvellous ! but it seems to need too much time to be comprehended and applied. We hoped to be done with these results and start already writing the paper :) Thank you very much for Your help !!! Sincerely, Alex. Le 04/12/2012 6:44 PM, Martin Reuter a écrit : > Hi Alex, > > I am not familiar with the way Doug describes the repeated measure anova > on the wiki. Of course in a longitudinal setting repeated measures are > correlated and I am not sure if this is considered in that model there. > > Since you have only 2 time points, why not simply compare the difference > (or weighted by the time distance, if the time points are not the same > distance apart)? > > You would compute (tp2-tp1)/time for each subject and then compare this > across groups with a standard glm. > Since in the longitudinal stream both thickness maps are registered, you > can simply use mris_calc to compute the difference directly. > > There are also scripts for this (long_mris_slopes, even for more than 2 > time points, where we fit a line into each subject). See the > http://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/LongitudinalTutorial > This is a simple approach, first reducing the variable of interest > (change across time) to a single number per subject and then running a > standard test. It should be sufficient for your setting. > > You can also do more complex modeling using our new linear mixed effects > models if you want (see older email from Jorge about that). It considers > both temporal and spacial correlation of measures. This model is > especially useful if you have differently many time points and time > distances per subject. > > Best, Martin > > > On Tue, 2012-12-04 at 18:26 -0500, Alex Hanganu wrote: >> Dear Freesurfer Experts, >> >> We are analysing longitudinal data - the difference between 2 groups (P >> and M) [19 and 17 subjects] with 2 time points for each group (A, B). >> >> We are using the example of "Repeated Measures Anova" >> (http://surfer.nmr.mgh.harvard.edu/fswiki/RepeatedMeasuresAnova) >> >> For our first approach - we took all the subjects - 36 classes, and >> tried to create the contrast for: >> >> P(B-A) - M(B-A) >> 2 within subject factors, and 2 inter-subject >> >> We considered the recent explanations >> (http://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg25459.html), >> and, as we understood, our null hypothesis is: >> >> PB-PA=0 AND MB-MA=0 -> >> Combining: PB-PA-MB+MA=0 >> >> and the matrix seems to be: >> 0 0 0 .... (36 zeros) -1 >> 0 0 0 .... (36 zeros) 1 >> 0 0 0 .... (36 zeros) 1 >> 0 0 0 .... (36 zeros) -1 >> >> but we still get a dimension mismatch between X and C: X has 72, C has 37. >> >> The fsgd file is like this: >> Class subject 1 >> . >> . >> . >> Class subject 36 >> Variables TP1-vs-TP2 >> Input groupPsubj1-A Subject1 -1 >> Input groupPsubj1- B Subject1 1 >> Input groupPsubj2-A Subject2 -1 >> . >> . >> . >> Input groupMsubj35-A Subject35 1 >> Input groupMsubj35-B Subject35 -1 >> Input groupMsubj36-A Subject36 1 >> Input groupMsubj36-B Subject36 -1 >> >> ============== >> >> Our second approach - we run mris_glmfit for each group separately and >> then we wanted to use mris_calc to compute the difference: >> >> mris_calc -o avg.mgh groupP/glm-dir/Contrast/sig.mgh add >> groupM/glm-dir/Contrast/sig.mgh >> >> though the sig.mgh for each group shows significant results, the avg.mgh >> reveals no effect. >> >> Can you please help with this analysis ? >> >> Thanks! >> >> Sincerely, >> Alex. >> ____________________ _______________________________________________ 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.
