Hi, Rick 1. The proportion is calculated as expected mean. If many positive cases are allocated in a pool , the efficiency can reach a tenfold even though the probability is low. Because COVID-19 presents high contagious, it is possible for infected cases to be tested one by one. 2. Will the sample be diluted in pool testing and how does it influent test efficiency and optimal k estimation? It maybe another topic to be considered in clinical practice.