....:j OPTIMAL GROUP TESTING IN THE PRESENCE OF BLOCKERS by

Testing in groups can lead to great efficiencies in total testing cost when searching for individuals with some characteristic. If the presence of a blocking object can cause a group with a positive object to test negative, there is a need to find optimal pooling strategies to minimize the cost of testing and reduce the number of missed positive individuals. We develop application driven cost functions to determine optimal testing strategies. Also, formulas are derived that describe the behavior of three different grouping strategies and provide examples illustrating how to determine the optimal strategy. We show that the strategies resulting from these methods provide much lower expected cost than classical methods. These results can be directly applied to HIV blood testing and for screening compounds for potential drugs.