design, blocking is a technique
used to deal with nuisance factors that
may affect the results of the experiment.
The experiment is organized into blocks,
where the nuisance factor is maintained
at a constant level in each block.
Suppose that the raw material needed for
the experiment is supplied in batches and
that there is insufficient material in a
single batch to carry out all the runs in
the experiment. To avoid the results being
affected by possible differences in the
material properties between batches the
experiment could be divided into blocks,
the material for each block being taken
from the same batch.