Optimal Two-Stage Sequential Sampling Plans by Attributes

Acceptance sampling plans have been widely used in statistical quality control for several decades. However, when nearly perfect quality is needed, their practicability is questioned by practitioners because of required large sample sizes. Moreover, the majority of well-known sampling plans allow nonconforming items in a sample, and this contradicts the generally accepted “zero defect” paradigm. Sequential sampling plans, introduced by Wald [7], assure the lowest possible sample size. Thus, they are applicable especially for sampling products of high quality. Unfortunately, their design is rather complicated. In the paper we propose a simple, and easy to design, special case of sequential sampling plans by attributes, named CSeq-1 sampling plans, having acceptance numbers not greater than one. We analyze the properties of these plans, and compare them to the properties of other widely-used sampling procedures.