Process Analysis Sampling Plans - General Purpose

A common challenge that quality control engineers face is to determine how many items from a batch (e.g., shipment from a supplier) to inspect in order to ensure that the items (products) in that batch are of acceptable quality. For example, suppose you have a supplier of piston rings for small automotive engines that your company produces, and your goal is to establish a sampling procedure (of piston rings from the delivered batches) that ensures a specified quality. In principle, this problem is similar to that of on-line quality control discussed in Quality Control. You may want to read the Introductory Overview at this point to familiarize yourself with the issues involved in industrial Statistical quality control.

Acceptance sampling
The procedures described here are useful whenever you need to decide whether a batch or lot of items complies with specifications without having to inspect 100% of the items in the batch. Because of the nature of the problem - whether to accept a batch - these methods are also sometimes discussed under the heading of acceptance sampling.
Advantages over 100% inspection
An obvious advantage of acceptance sampling over 100% inspection of the batch or lot is that reviewing only a sample requires less time, effort, and money. In some cases, inspection of an item is destructive (e.g., stress testing of steel), and testing 100% would destroy the entire batch. Finally, from a managerial standpoint, rejecting an entire batch or shipment (based on acceptance sampling) from a supplier, rather than just a certain percent of defective items (based on 100% inspection) often provides a stronger incentive to the supplier to adhere to quality standards.