An allocation scheme for estimating the reliability of a parallel-series   system
  We give a hybrid two stage design which can be useful to estimate the reliability of a parallel-series and/or by duality a series-parallel system, when the component reliabilities are unknown as well as the total numbers of units allowed to be tested in each subsystem. When a total sample size is fixed large, asymptotic optimality is proved systematically and validated via Monte Carlo simulation. 
Zohra Benkamra, Mekki Terbeche, Mounir Tlemcani
stat.AP