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Hi all, I have a question concerning the weighting function in the gPPI toolbox found at http://www.nitrc.org/projects/gppi. Our lab would like to utilize gPPI to examine differences in connectivity between two trial types in our latest experiment, trial type A and trial type B. Our trial types are, however, dependent on participants behavior and differ in the average number of trials per trial type. For example, trial type A averages 40 trials across participants and trial type B averages 20 trials across participants. After doing some research and talking to colleagues, it seems that the gPPI toolbox offers a "weighted" option to weight different trial types based on the number of trials. The gPPI manual found at the above link provides the following explanation for using the weighted option: Default is not to weight tasks by number of trials (0); to change this, specify which tasks should be weighted by trials. If you want to weight trials, then specify a duration longer than your events. If you have a mixed block event related design, then you can average your events based on number of trials and the blocks won't be averaged IF Weighted is set to be a number that is shorter than the block duration and longer than your events. I was wondering if someone could clarify how this option works and how best to apply it to the current situation (or if there is another option). From what I can gather, it seems like I should set this weighted option to a number greater then the duration of our events (the duration of our events is 0), but does the number matter? Would it matter if I set this option to 1 vs. 5 vs. 20? I do not understand why the toolbox would need to take trial duration into account to weight by number of trials. Thanks all. Best, Kyle -- Kyle Andrew Kurkela CAN Laboratory Manager Department of Psychology Pennsylvania State University 441 Moore Building "The problem, often not discovered until late in life, is that when you look for things like love, meaning, motivation, it implies they are sitting behind a tree or under a rock. The most successful people recognize, that in life they create their own love, they manufacture their own meaning, they generate their own motivation. For me, I am driven by two main philosophies, know more today about the world than I knew yesterday. And along the way, lessen the suffering of others. You'd be surprised how far that gets you." - Neil deGrasse Tyson, Astrophysicist.