An analysis of the long range operating characteristics of the MIL-STD-105D sampling scheme and some suggested modifications

摘要

An integral part of the MIL-STD-105D scheme for sampling inspection by attributes isthe transfer from normal inspection to reduced or tightened inspection when the historicalrecord of inspected lots suggests unusually good or bad quality. The switching rules inMIL-STD-105D have been criticized, especially by Japanese manufacturers, as being toosevere when what is defined as acceptable quality material is submitted. This paper examinesthe long range fraction of lots rejected for several MIL-STD-105D sampling plans by usingthe MIL-STD-105D switching rules, using a modification suggested by the JapaneseStandards Association, and by using a second modification developed by the authors.The Japanese Standards Association switching rules are more complex than those inMIL-STD-105D. It is demonstrated that they lead to improved long-range properties forNormal-Tightened-Reduced schemes, but to poorer properties for Normal-Tightenedschemes. A simplified set of switching rules is suggested, wherein the “limit numbers” in MIL-STD-105Dare eliminated. In comparison to MIL-STD-105D, the simpler rules lead to alower probability of rejection for good lots and a comparable probability of rejection forbad lots.