help > RE: Is small cluster size problematic?
Jul 12, 2018  10:07 PM | Alfonso Nieto-Castanon - Boston University
RE: Is small cluster size problematic?
Hi,

The details of your second-level analysis specification all seem perfectly correct, but yes, it is possible that the issue might be related to the custom smoothing process. Generally if the images are not sufficiently spatially smoothed, and/or if the level of smoothing is not homogeneous across the entire volume, that might cause problems with some of the Random Field Theory assumptions underlying the parametric cluster-estimation procedure (again pointing to either applying additional spatial smoothing to your data or using non-parametric stats in order to validate your results)

Hope this helps
Alfonso
Originally posted by wzhong:
Hi Alfonso,

I should note that I performed the preprocessing steps including denoising and smoothing outside conn in a custom in-house pipeline, then I imported the data into conn using batch scripting skipping preprocessing and denoising steps. In my preprocessing I used 3dBlurToFWHM smooting with a kernel size of 6mm.

Would this have caused problems for smoothing when importing into conn? I also have non-smoothed, denoised image files, should I have used these in the conn analysis and used smoothing in conn? If these do not work I will try nonparametrics.

I ran the second level as follows:

Subject effects: [AllSubjects behav age_mean_centered male female mean_fd], contrast = [0 1 0 0 0 0]
   Where behav is the outcome measure of interest (it is a continuous measures with a fairly small range between 1 and 10 and is not mean-centered); for the covariates, age has been mean centered, male and female are two binary indicators with values of 0 or 1 for being male or female (and vice versa), and mean_fd is the subject motion measure (not mean-centered since I think 0 is meaningful here indicating subjects without motion).

Conditions: Rest [1]

For Sources I entered my ROIs of interest and run a F-test contrast (eye(n)). I also tried running separate t-tests for each source ROI and bonferroni correct for the cluster FDR alpha-level, the resulting clusters are all small.

Thanks!

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TitleAuthorDate
wzhong Jul 6, 2018
Alfonso Nieto-Castanon Jul 11, 2018
wzhong Jul 11, 2018
RE: Is small cluster size problematic?
Alfonso Nieto-Castanon Jul 12, 2018