About PBIB(3) Designs
Balanced Incomplete Block (PBIB) designs form an important class of incomplete
block designs in which variance of every estimated elementary contrast among
treatment effects is not same. The variances depend on the underlying
association scheme of the design. The two-associate class PBIB [PBIB(2)] designs
are available in Clatworthy (1973). For a given parametric combination, a
PBIB(2) design may not exist or if exists, it may require too many replications.
A PBIB(3) design can be an alternative in such situations.