Dear FSL users,
We have run a study with 17 participants, each with 3 runs. After running
our models on each run (lets say 3 EV’s per run), we combined the 3 runs per
subject under a fixed effects framework. We then combined the resulting
COPE files using FLAME 1&2 and threshold at Z=2 and cluster p<.05.
In reviewing the results, we find very few, if any, significant voxels in
the thresh_zstat images. However, when reviewing the zstat images, there
are quite a few voxels (and only in a priori, hypothesized regions) with z’s
above 2.0. We assume that the cluster correction is the sole or primary
source of the lack of significance. Is this correct?
We have tried running the analyses using FLAME 1 with the same results. We
also tried running the data under a Fixed effects framework for exploration
purposes. This obviously led to far more identified voxels, but running
Fixed effects analyses are not appropriate at this stage.
We have several questions.
Is it correct to interpret this pattern as resulting from just sub-threshold
activation/effects?
Might there be a problem we are missing?
Would it be appropriate to report any statistics or findings from the
uncorrected zstat images in a write-up of results? (for example, voxels with
z-values above a certain number?)
Short of collecting more data (which is not an option), do you have any
suggestions?
We have been working on analyzing the data using ROI analyses to work around
the relatively stringent correction in whole brain analyses but suggestions
will be appreciated.
|