We study the group test for DNA library screening based on probabilistic
approach. Group test is a method of detecting a few positive items from among a
large number of items, and has wide range of applications. In DNA library
screening, positive item corresponds to the clone having a specified DNA
segment, and it is necessary to identify and isolate the positive clones for
compiling the libraries. In the group test, a group of items, called pool, is
assayed in a lump in order to save the cost of testing, and positive items are
detected based on the observation from each pool.