Reliability is an important consideration in the planning, design, and operation of engineering systems.

The benefits of reliable systems are enormous and include a reduction in unexpected failures, lower main-

tenance costs, lower life-cycle costs, improved safety, less need for in-process inventory to cover downtime and

more consistent quality [1,2]. Prior to World War II, the concept of reliability had been intuitive, subjective,

and qualitative. Today, it is a well-recognized discipline with many specialized areas, including that of human

reliability, robot reliability, software reliability, and mechanical reliability.