**Block**: A level of a random factor
designated to sample unmeasured spatial or temporal variation in the
environment. For example, a field that slopes north to south might be
partitioned into horizontal blocks (running east-west) so that the blocking
factor contains the unmeasured variation due to slope and thereby minimizes the
within-block residual variation. In a
randomized complete
block, each level of the treatment factor (or each combination of levels in
the event of two or more factors) is randomly allocated to one plot in each block. The
Latin Square is a variant on this design for
two blocking factors.

Doncaster, C. P. & Davey, A. J. H. (2007) *Analysis of Variance and Covariance: How to
Choose and Construct Models for the Life Sciences*. Cambridge: Cambridge
University Press.

http://www.southampton.ac.uk/~cpd/anovas/datasets/