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July/August 2008
Feature

Stats for Quality Control

ASTM Committee E11 on Quality and Statistics largely develops standards that show the correct use of the principles and methods of statistics and quality control in the development, application and improvement of other standards. But Subcommittee E11.30 on Statistical Quality Control also develops standards used by manufacturers to help ensure process control, such as these two practices.

  • E1994, Practice for Use of Process Oriented AOQL and LTPD Sampling Plans — AOQL, or average outgoing quality limit, is the greatest defective or defect rate that should go out to the customer over an extended period of time. LTPD, or lot tolerance percent defective, is that level of quality that the sampling plan will accept 10 percent of the time. E1994 gives users guidance in the use of these sampling plans, providing an abbreviated compilation of the sampling plans developed by Harold F. Dodge (Committee E11’s first chairman) and Harry G. Romig, two luminaries in the science of statistical quality control to emerge from Bell Laboratories in the mid-20th century.
  • E2234, Practice for Sampling a Stream of Product by Attributes Indexed by AQL — AQL is the worst-case level of quality considered acceptable. Based on a U.S. military standard, E2234 establishes lot or batch sampling plans and procedures for inspection by attributes when sampling a steady stream of lots indexed by AQL. The standard guides the user in developing an inspection strategy that provides a cost-effective approach to attaining confidence in product compliance with contractual technical requirements. The sampling plans can be used in quality assurance for end items, components and raw materials, operations or services, materials in process, supplies in storage, maintenance operations, data or records and administrative procedures.

In addition to developing standards and helping other technical committees with their statistics-related efforts, Committee E11 sponsors workshops, seminars and symposia that advance the state of the art of using statistics and quality control methods in standards.

Look for a statistics question-and-answer column starting in the next issue of SN. E-mail your questions about statistics and developing ASTM International standards to Editor in Chief Maryann Gorman.

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