Fig. 2.

Configuration for three-stage hierarchical testing with an initial pool N. The number of the groups or the divisions of the N population is termed as Xi (1 < i < N). Yij is the number of the samples in each pool (1 < i < N, 1 < j < N) and is the same for all the pools. Xi pools are examined individually. Upon a negative result of the Xi, all the Yij can be declared healthy. If the result is positive, then sub-pools of its members are formed for a second stage of testing, to isolate those that contain positive samples. Consequently, if a sub-pool is positive, then individual testing of all its members is going to be implemented in the third and final stage.