[R] contrast reference level

array chip arrayprofile at yahoo.com
Thu Dec 2 23:42:06 CET 2004

suppose I have a factor with 4 levels:
'a','b','c','d'. I would like to do analysis of
variance using aov() with the factor as independent
variable. How can I specify the level "b" as the
reference level just like the level "a" would be the
reference level if using contr.treatment as the


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