Dear freesurfer experts:
We are using freesurfer to preform a cortical thickness analysis between patients and controls. We plan to use the mean_thickness and subject age as covariates. It's fine to analysis as group x age or group x mean_thickness, respectively. But when we set design as group x age x mean_thickness, an error report appeared in the terminal: -------- Matrix condition is 11355.6 ERROR: matrix is ill-conditioned or bad scaled, condno = 11355.6 Possible problem with experimental design: Check for duplicate entries and /or lack of range of continuous variables within a class. (continuous with values in Xg.dat) ------
Does the problem course by the different "range" from age value (between 18-28) and mean_thickness (between 2-4) with in the same subject? if so, how can we solve it? Does proportional scaling on age or mean_thickness help?
Any comments are welcome and very appreciate.