Dear Freesurfer,
The following is a follow-up, on a previous discussion (http://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg51582.html) but i am still left with some uncertain and unanswered questions.
My design: Patients and Controls, MRI scanned at baseline and after 6 weeks (only two time points). The average follow-up time is about 7 weeks when using the exact time.
1) I understand that the if you pass the --generic-time in the long_stats_slopes command, the 'time' column should not be in the qdec table as it assumes the values are 1,2,3,4 (subjects are ordered in TP1, TP2). However, if there is an exact time, then a 'time column' should be in the qdec table and the --generic-time should not be passed in the long_stats_slopes command. Is this correct?
2) If the exact time is not present, how is the symmetrized precent change calculated? Since it is calculated spc = 100 * rate / avg, and rate is calculated: rate = ( thick2 - thick1 ) / (time2 - time1) then there must be a time right?
Thanks in advance. I hope some of you have find the time to help :-) I am a little stuck with these details.
Best regards, Kasper
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