Dear list, Is it possible to specify a contrast in options() that would create an identity matrix for each factor in the model matrix? For example, for each factor in 'dd' below, I can create an identity matrix using contrasts = FALSE. Is it possible to set this in options(), so when I create a model matrix from any factor, the factor coding would follow this specification for the contrast? dd <- data.frame(a = gl(3,4), b = gl(4,1,12)) ca <- contrasts(dd$a, contrasts= FALSE) # 3 x 3 identity matrix cb <- contrasts(dd$b, contrasts= FALSE) # 4 x 4 identity matrix My attempt below works fine, but again, I'd like to specify this in the options() as opposed to each contrast individually. model.matrix(~ a + b, dd, contrasts =list(a=ca, b=cb)) Thanks for any help! Axel. [[alternative HTML version deleted]]