In Chapter 1 we defined failure of a product (or system) as the inability of the product to perform its stated function and discussed the consequential customer dissatisfaction resulting from such failures. The customer's view of whether or not product performance is satisfactory depends on their needs and expectations. Product performance is influenced by the following two sets of factors:
- Factors prior to the sale of the product: These are primarily technical and engineering factors related to the design, development, and manufacturing of the product. The manufacturer has reasonable control over these factors and in some cases (for example, defense acquisitions) the customer may have a significant influence.
- Factors during use: These relate to the environment and the mode of usage. The latter includes factors such as duty cycle, intensity of usage, etc. The performance of a product ordinarily degrades as the environment becomes harsher and/or the usage intensity increases. These factors are, to a significant degree, under the control of the customer, and the manufacturer has very little (and often no) control over them.
For most products, the characterization of product performance requires a multidimensional vector. Several components of this vector are related to product reliability. These include various notions of reliability, dependability, availability, and so on. Some of the reliability-related performance measures, ...