ZhiLiangLong wrote:
Hi doug Thanks for your suggestions. I have another two questions: 1: I can't clearly understand that why i should firstly run DODS to find interaction between my group variables and age,then run DOSS to obtain difference between groups specified in my contrast files if there are no interactions as you suggested.If the interactions exist,does it mean that DOSS is not suitable for this situation and only DODS can be used ?
If there is an interaction, then DOSS is not suitable because there is no simple difference between the groups.
2: If i want to obtain the main effect of factor(difference between the three groups),how can i setup my contrast file?
Do a search on our Wiki for FSGD. There's a page of examples there, including an example of your current design. doug
Hope you can give me some suggestions
At 2011-10-12 00:21:34,"Douglas N Greve" greve@nmr.mgh.harvard.edu wrote:
Yes, that looks correct. Since you have a covariate as a nuisance variable, you should first run your analysis with a DODS model (different-offset, different-slope) and look for an interaction between your group variables and age (the contrasts are similar, swap the first 6 numbers with the last 6 zeros). If you do not find an interaction, then re-run the analysis with DOSS and use a contrast that has 7 numbers: the first 6 as you have given, the last number = 0.
doug
ZhiLiangLong wrote:
Hi all : I'm performing general linear model (GLM) analysis in the surface,the attachments above are FSGD file and contrast files(the last three attachments).i wonder if my contrast files are correct. the attachment named diff-C-H-thickness.txt is about difference between C and H and the last two are about difference between C and p and difference between P and H,Here,C H and P represent three groups Any suggestions appreciated
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