Hi Douglas, thank you for the explanation of the contrasts, this helped a lot!
All the best, Kai 2018-03-12 18:20 GMT+01:00 Douglas N. Greve <dgr...@mgh.harvard.edu>: > Yes, let's say you have 4 groups (eg, gender and sequence) and one > covariate (BDI score). If you use a DODS model, then you will have 8 > regressors (4 intercepts and 4 slopes). To test for an effect of covariate > regressing out the group, then you would have > > [0 0 0 0 .25 .25 .25 .25] > > The +0.25 computes the mean slope across all groups (note you could also > just use all 1s, you will get the same p-value). > > > > On 03/09/2018 01:43 PM, k.ohmst...@stud.uni-heidelberg.de wrote: > >> Hi Douglas, >> >> thanks for the advice. >> >> I have one more question: I want to find correlations of the lGI and the >> respective psychometric measurement, regressing out the effect of gender, >> sequence and the other covariates. >> I just had a look at the examples of FSGDs containing two factors with >> two levels each and as far as I understand it, it is only possible to >> compare two of the groups or to find an interaction between groups and >> covariates. >> >> Is it at all possible to find out how the lGI is correlated to one of my >> covariates, i.e. higher values of Beck's Depression Inventory correlate >> with higher/lower values of the lGI, when regressing out the other factors? >> If yes, how do I build the contrast file to do so correctly? I am stuck >> here. >> >> Thank you for the time and effort! >> >> >> Best regards >> >> Kai >> >> Zitat von Douglas Greve <dgr...@mgh.harvard.edu>: >> >> Hi Kai, please remember to post to the list. Your FSGD file is not >>> quite right. Gender is a discrete variable and should be represented by >>> two groups not as a covariate. If Sequence is discrete, then you need >>> four groups (Gender by Sequence). >>> >>> doug >>> >>> >>> On 3/9/18 3:20 AM, k.ohmst...@stud.uni-heidelberg.de wrote: >>> >>>> Dear Douglas, >>>> >>>> the fsgd file I used is attached. Thank you for your help! >>>> >>>> >>>> Best regards >>>> >>>> Kai >>>> >>>> Zitat von "Douglas N. Greve" <dgr...@mgh.harvard.edu>: >>>> >>>> can you send your fsgd file so that I have a better idea of what you are >>>>> mentioning? >>>>> >>>>> >>>>> On 03/08/2018 08:39 AM, k.ohmst...@stud.uni-heidelberg.de wrote: >>>>> >>>>>> Dear all, >>>>>> >>>>>> I am trying to correlate psychometric measurements and the local >>>>>> Gyrification Index. >>>>>> To do so, I use the FreeSurfer pipeline to calculate the lGI and then >>>>>> PALM, following the advice in this thread >>>>>> (https://mail.nmr.mgh.harvard.edu/pipermail//freesurfer/2017 >>>>>> -March/050703.html). All my subjects are part of the same group, so >>>>>> I used a FSGD with the >>>>>> group "main" to create the design matrix and mask for my data that are >>>>>> required by PALM. >>>>>> Having a closer look at the design matrix that was created, I found >>>>>> that there was a variable for the group that was the same for all my >>>>>> patients. As it is the same for all patients, I thought eliminating it >>>>>> would not be a problem. But after re-running PALM without it, there >>>>>> were huge differences in my results and effects were notably larger >>>>>> and more significant. >>>>>> >>>>>> Do any of you have any experience which option is best in this case? >>>>>> Is it a valid choice to eliminate the variable for the group, as it is >>>>>> the same for each patient anyway? >>>>>> >>>>>> Furthermore, would you recommend centering for the design matrix? I >>>>>> found that this can have an impact, but I am lost on in which cases it >>>>>> should be done and in which it shouldn't. >>>>>> >>>>>> >>>>>> Thank you for your help! >>>>>> >>>>>> >>>>>> Best regards >>>>>> >>>>>> Kai Ohmstedt >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> Freesurfer mailing list >>>>>> Freesurfer@nmr.mgh.harvard.edu >>>>>> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >>>>>> >>>>> >>>>> _______________________________________________ >>>>> 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. >>>>> >>>>> >>>>> >>>> >>>> >> >> >> >
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