Toward a determination of optimal multilevel sampling plans

Traditionally continuous sampling plans have been evaluated according to relatively few criteria. These typically include the OC curve (on which AQL systems are based), the ASN, and the AOQ curve. These characteristics are all calculated under the assumption that the process is “in control” so that mathematically they are derived as long-term averages. Thus, any two plans which (long term) spend the same proportion of time on each type of sampling inspection will be identical relative to these criteria. This is true whether sampling from lots or doing unit-by-unit inspection. The goal is to first establish desirable additional criteria and then to develop methods to determine which procedure (of those which satisfy the standard criteria) is optimal relative to the new criteria. To be considered will be measures of a plan's ability to detect a sudden drop in quality (such as ARL).