A method used in the Design
of Experiments. Suppose we
wanted to compare four brands of washing
powder. We decide to carry out four replications
for each brand. To make the test realistic
we give four volunteers four clean handkerchiefs
each; they are to use each for one day.
In a Completely
Randomized Design we would
allocate the handkerchiefs to powder at
random, so that one powder might get one,
two, three or even all four handkerchiefs
from one person.
In a Randomized Block design we would block
on the handkerchiefs. We would allocate
one, and only one, handkerchief from each
volunteer to each powder.