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Hi - how different are they? Is it just a factor of two - i.e. in one case you're assuming two-tailed testing and in the other one-tailed? Cheers. On 8 Jun 2010, at 15:48, wolf zinke wrote: > Hi, > > I hope this is not an obvious stupid question ;-) . I want to prepare data for an FDR correction, which requires an image of p values as input. The FDR website describes how to obtain a p-value image by using ttologp with the varcope and cope files as input and feeding the resulting file into fslmaths with the -exp option. I was now wondering if I could not just transform the available z-value image to a p-value image just by using one fslmaths call with the -ztop option. However, the p-value images of both methods are not identical. What is the difference between both methods? Is it possible to transform just the zstats to prepare the data for an FDR correction? > > Thanks for any comments, > wolf > --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------