contrast Helmert contrast Philippe Rocca-Serra Alejandra Gonzalez-Beltran Orlaith Burke A Helmert contrast is a contrast in which the coefficients for the Helmert regressors compare each level with the average of the “preceding” ones contr.helmert(n, contrasts = TRUE, sparse = FALSE) http://stat.ethz.ch/R-manual/R-patched/library/stats/html/contrast.html http://www.clayford.net/statistics/tag/helmert-contrasts/ An R and S-Plus Companion to Applied Regression. John Fox ISBN-13: 978-0761922803 requires discussion