data item contrast weight Alejandra Gonzalez-Beltran Camille Maumet Orlaith Burke Philippe Rocca-Serra Thomas Nichols a contrast weight is a coefficient which multiplies a group mean, part of a linear combinaison defining a constrast as a weighted sum of group means, giving a 'weight' to a specific group mean hence the name. adapted from wikipedia: http://en.wikipedia.org/wiki/Contrast_%28statistics%29 contrast coefficient http://artax.karlin.mff.cuni.cz/r-help/library/nparcomp/html/weight.matrix.html ready for release