Hi Ann-Kathrin,

for age you should use age at baseline (should be fixed for all time points per subject). You have the time_from_baseline variable to model the time. (maybe that is what you are already doing).

I don't know why more survives with the voxelwise model, I usually see the opposite, but of course you can use the voxel wise approach with FDR correction in your analysis.

Best, Martin

Am 16.08.2017 um 12:01 schrieb Ann-Kathrin Rogge:

Dear freesurfer experts,

I have a mixed 2x2 design with group (approx. 18 subjects per group) and timepoint (t0, t1) as factors. I analyzed the thickness data with the longitudinal stream and the spatiotemporal LME as a random intercept model, age as covariate. However, the model does not converge perfectly, although I varied the size of the homogenous covariance regions between 1-2 (parameter k, Bernal-Rusiel et al., 2013). In addition, when I apply a voxelwise-LME, more clusters survive the FDR correction. It seems that the V-LME is more sensitive than the SP-LME in my case (clusters at an uncorrected threshold are more or less the same). I would love to understand why. Could anyone explain this to me? And would it be statistically valid to apply the V-LME to my data?

Best,

Ann-Kathrin

-- *Ann-Kathrin Rogge, Dipl.-Psych.* www.bpn.uni-hamburg.de

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