Duncan's procedure is similar to the Newman-Keuls
procedure. The difference is that the critical values are much more
liberal. The goal of Duncan's procedure is to keep the
EER at
where "a" is the number of means and is the PCER.
This level of EER can be unacceptably high, however. With six means and
a per comparison error rate of 0.05, the EER is 0.23. Duncan's procedure
is only very slightly more conservative than Fisher's
LSD. In practice, they almost always lead to the same conclusions.