1. The optimal level of inspection balances the cost of inspection and the cost of allowing undetected defectives to pass through the system.

2. Each situation calls for a different type of inspection process; the stages of production where inspection may take place include: raw materials and purchased parts, finished product end items, before costly operation, before taking an irreversible step, or before painting or plating or some other covering that hides potential defects. Also some inspections take place at the production site and others at the customer's designated location, or in a laboratory.

3. Acceptance sampling pertains to incoming batches of raw materials (or purchased parts) and to outgoing batches of finished goods. Current emphasis in quality assurance is away from acceptance sampling and towards 1) improving the process so that there is less need for inspection, and 2) improving supplier quality so that there is less need for inspection of incoming goods.

4. Acceptance sampling can be applied to either attributes or variables. Attributes are those characteristics of a product or service that are counted (e.g., pass-fail, defective-nondefective), and variables are characteristics that are measured (e.g., width, thickness, weight).

5. The technical starting point for an acceptance-sampling plan is the operating characteristic (OC) curve, which gives probability of acceptance, P_acvs. quality level (i.e., the proportion of defects p). The higher p is, the lower <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image258.gif::/sites/dl/free/0072443901/24520/Image285.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image258.gif (0.0K)</a>Image258.gif is. A widely used type of OC curve has two clearly identifiable points:

1. The Acceptable Quality Level (AQL) is a designated low percent of defective items.
   For the AQL, <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image286.gif::/sites/dl/free/0072443901/24520/Image286.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image286.gif (0.0K)</a>Image286.gif , where <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image287.gif::/sites/dl/free/0072443901/24520/Image287.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image287.gif (0.0K)</a>Image287.gif is the probability of rejecting a lot with an AQL percent of defective items.
2. The Lot Tolerance Percent Defective (LTPD) is a designated high percent of defective items..

For the LTPD, <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image288.gif::/sites/dl/free/0072443901/24520/Image288.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image288.gif (0.0K)</a>Image288.gif , where <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image289.gif::/sites/dl/free/0072443901/24520/Image289.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image289.gif (0.0K)</a>Image289.gif is the probability of accepting a lot with an LTPD percent of defective items.

6. The AOQ is the average outgoing quality, frequently shown as a curve with AOQ as a function of p. When rejected lots are inspected 100 percent to remove all defective items and the defectives are replaced with good items, the AOQ is better than with intermediate quality lots because of the extra inspection.

For lots where the number sampled, n, is small relative to the lot size, N, the <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::Image290.gif::/sites/dl/free/0072443901/24520/Image290.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif">Image290.gif (1.0K)</a>Image290.gif
The highest AOQ (poorest outgoing quality) for a sampling plan is known as the average outgoing quality limit or the AOQL.