Читать книгу System Reliability Theory - Marvin Rausand - Страница 17

In our daily language, the term “reliability” is used to describe both past and future behavior. We may, for example, say that (i) “my previous car was very reliable” and (ii) “I believe that my new car will be very reliable.” These two statements are quite different. The first statement is based on experience with the car over a certain period, whereas the second statement is a prediction of what will happen in the future. We distinguish them by using two different terms.

 Reliability (single word) is always used to describe the future performance of an item. Because we cannot predict the future with certainty, we need to use probabilistic statements when assessing the reliability.

 Achieved reliability is used to describe the item's past performance, which is assumed to be known to the analyst. No probabilistic statements are therefore involved. The achieved reliability is also called observed reliability.

The focus of this book is on reliability and the future performance. The achieved reliability is most relevant in Chapter 14, where analysis of observed failure data is discussed.