Probability with R, 2nd Edition

14Sampling Inspection Schemes

14.1 Introduction

When products are manufactured, they are often packed in batches and subjected to a quality test before delivery to the customers. A sample of products is taken from each batch and examined for defectives. A decision to reject or accept the batch is made on the basis of the number of defective items in the sample. If too many defectives are found in a sample, the batch is rejected. After that, it may be sold off cheaply or subjected to a 100% inspection.

Sampling inspection schemes may differ with respect to the sample size taken from each batch, the allowable number of defectives, and the post inspection action. In this chapter, we look at some such inspection schemes.

Samples are usually taken, rather than a complete inspection of the products, in order to save time and money. Of course, in the case of destructive testing, in which the inspection process involves damage to the product so that it cannot be used again, sampling is essential, and it is important to keep the sample size as small as possible, while maintaining adequate monitoring of the quality of the products.

In contrast, in precision engineering and dependable systems, it is more common to inspect every item, in which case there are few statistical problems, and most of the following remarks do not apply.

14.2 Single Sampling Inspection Schemes

Example 14.1

A certain item is packed 100 to a box. Before distributing to the retailers, each box is subjected to a ...