Sampling Plans with Low Consumers' Risk

Abstract

Most sampling activity is concerned with the Acceptable Quality Level (AQL) or Producers' Risk. There exists, however, applications for sampling schemes built around the Limiting Quality Level (LQ) or Consumers’ Risk. Examples include isolated lots or cases where the characteristic being examined in the sample is so severe that extra care must be taken to prevent nonconformances being shipped or used. When the output of nonconformances must be zero or measured in parts per million, a sampling scheme with low consumers’ risk can be effectively used to audit a process. It can be argued that this is a form of process control because rejection of a lot under this scheme is an indication of major problems. In such cases, diagnosis and corrective action are required immediately, in addition to the usual screening of the rejected lot and those immediately preceding it. This paper provides such a sampling scheme. The determining parameter is the average outgoing quality limit (AOQL). LQ's from 0.001 to 0.05 are used. Because of the universal application and popularity of MIL-STD-105D and the ANSI Standard Z1.4 (Ref.), their format and procedure have been followed wherever possible.