External Email - Use Caution Dear FreeSurfer experts,
I have two groups and two time points and I would like to do a correlation analysis between a variable (cognition) and the change score in cortical thickness between the two time points (time2 minus time1). I would like to see if the *correlation *is *different *among each group, if there is an interaction with the group. I have followed the paired t test instructions ( https://secure-web.cisco.com/11YHUupGYyGBe5w6QAQb3OOLcNluK0Tqv4VUmAmDx5wuogvWlaypoD3OpvEWBM2c4Wa29T38k5k4_bq_JXA-kc8P0mACbCulAMmVSDKvC4Tl7x6Gk2A_azFExScL0y5HFngabH5bZRoIDy_dKvAtXkXegvTr-2ftNMkD3TQlTwaQtCSI-0554BriqrUu1MKXy2ZDf8l6cSP5im59p93FqJma0yYa3cYXujDp-aXCIOKlUXzojlgBIskwrWMiPG0pmIn08tOj1OYgSExrdJrOrWu2iAIGdhvSK3iuWEQ7BCEp4De-DPfIldNoZfbygVQ1mrt9CvPacDWwenDkjC7Q40A/https%3A%2F%2Fsurfer.nmr.mgh.harvard.edu%2Ffswiki%2FPairedAnalysis), but I am not sure about the contrast(s) I have to use. The paired-diff.fsgd file (second fsgd file) is the following: GroupDescriptorFile 1 Title OSGM Class Group1 Class Group2 Variables cognition Input subject1pair Group1 0.546 Input subject1pair Group2 -0.243 ... How should it be the contrasts files to see the *correlation *of the variable cognition with the change score in thickness taking into account the groups? And should I use DODS or DOSS? Using DODS: 0 0 0.5 0.5 or 0 0 1 -1 I don't understand the difference between both contrasts. I think I should use the one of "0 0 1 -1" to see whether the cognition variable correlates with change in thickness differently according to the group. Is this correct? Using DOSS: 0 0 1 Thank you very much in advance. Kind regards, Agurne
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