Dear Dorian, see inline comments... Am Mittwoch, den 28.01.2009, 11:50 +0100 schrieb Dorian P: > Une small addition: > > If I need to try modulation 1-2-3-4-5 and see the regressor effect > with contrast [0 1], > can I just run contrast [0 -1] to save another GLM with modulation 5-4-3-2-1 ? yes > > I have a simple question. I need to run around 5 GLMs for each subject > > (N = 19) with different parametric modulation values for different > > variables. > > My question is: Is there a way to save time by using some calculations > > previously done for the subject? > > > > I don't know the steps of a GLM, but thinking of SPM, it first > > establishes the number of resels and then runs the analysis, and > > thinking that the volumes to analyze are the same for each subject, > > and though number of resels should be the same... can this be useful > > to the next GLM? Any clue how to save time? No. Even if the number of voxels that are considered is the same, the smoothness of the error (and thus the number of resels) will depend on the model. However, you should model all effects that you expect to be in your data in a single model, not in separate models. There may be reasons to run 2 or 3 models (e.g. some experiments may be modeled either as block or event related), but there is no way to shorten the analysis time. Volkmar -- Volkmar Glauche - Department of Neurology [log in to unmask] Universitaetsklinikum Freiburg Phone 49(0)761-270-5331 Breisacher Str. 64 Fax 49(0)761-270-5416 79106 Freiburg http://fbi.uniklinik-freiburg.de/