In balanced incomplete block designs, each pair of treatments is compared with equal precision, and each treatment is paired with every other treatment an equal number of times with in a common block; A is a constant for all treatments. There is one associate class for each treatment in balanced incomplete block designs. These are the most important balanced incomplete block designs, but the need sometimes arises for others; either because no suitable balanced incomplete block design exists, or because, for example, it is necessary to make some comparisons more precisely than others. We can see balanced incomplete block designs form that special case of partially balanced designs in which there is one associate class for each treatment. In this paper, the author will discuss the partially balanced incomplete block design with two associate classes
