Appendix BIntroduction to Product Reliability

In the Preface, I presented the ISO 9000 definition of product quality as the degree to which a set of inherent characteristics of a product or service fulfils customer requirements. While speaking of the quality of a product or service, this definition says nothing about how long the quality will last. What is its durability? What good is the quality of the thing if it is gone by the time you get home?

Some products are meant to be disposable and their durability is not critical. Others might be expected to last a long time, such as appliances. The durability of some products is marked on the package, light bulbs being an example. I use the word durability because it is generally understood to refer to how long a product can be useful and the term is often used as a product characteristic. However, durability is not a technical term and has no meaning to engineers. It means whatever the manufacturer wants it to mean.

When referring to how long a product can meet intended requirements, engineers use the term reliability and define it rigorously (Grant & Leavenworth, 1988): ...

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