has part is about denotes is_specified_input_of is denoted by data item study group population model fitting factor level combination contrast A contrast is the weighted sum of group means, the c_j coefficients represent the assigned weights of the means (these must sum to 0 for orthogonal contrasts) Term request by Nolan Nichols via https://github.com/ISA-tools/stato/issues/9 contrasts(x, contrasts = TRUE, sparse = FALSE) http://stat.ethz.ch/R-manual/R-patched/library/stats/html/contrasts.html Alejandra Gonzalez-Beltran Camille Maumet Orlaith Burke Philippe Rocca-Serra Tom Nichols http://en.wikipedia.org/wiki/Contrast_%28statistics%29 contrast weight matrix average value requires discussion