contrasts(x) contrasts(x) <- ctr
x
 | a factor. | 
ctr
 | 
either a matrix whose columns give coefficients
for contrasts in the levels of x, or the (quoted)
name of a function which computes such matrices.
 | 
options("contrasts") are used.contr.helmert,contr.poly,
contr.sum,contr.treatment,
glm,lm.