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Hi, the minimum cluster allowable size depends on the t-threshold and the p-value (and the data). For a clear description of how non-parametric cluster thresholding works, you can see TE Nichols and AP Holmes Nonparametric Permutation Tests for Functional Neuroimaging: A Primer with Examples Human Brain Mapping, 15:1-25, 2001 Hope this helps Tim Tim Behrens Centre for Functional MRI of the Brain The John Radcliffe Hospital Headley Way Oxford OX3 9DU Oxford University Work 01865 222782 Mobile 07980 884537 [log in to unmask] www.fmrib.ox.ac.uk/~behrens On 17 Feb 2006, at 15:22, bas Jasperse wrote: > Dear FSL-list, > > Recently we started using randomise to perform voxelwise statistics on > SIENA displacement maps and are currently performing correlations > and group > comparisons. > > We also want to use cluster thresholding for our analysis, but are > a bit > puzzled by the option provided. > > The manual tells us that the only thing we can specify is <c_thresh>. > We assume that this means setting the supra-threshold based on the > T-stat image. Is this correct? > > There is no option provided for cluster size in voxels or mm, so we > were > wondering > if and how randomise sets the cluster size. Could you provide some > insight > in this matter? > > > We've tried searching the Jiscmail archives, but could not find an > answer > to these issues. > > Thanks in advance for your help, > > kind regards, > > Bas Jasperse > Vu medical centre, Amsterdam