Importance of system components and fault tree events

A new measure of the importance of the components in a coherent system and of the basic events in a fault tree is defined and its properties derived. The importance measure is a useful guide during the system development phase as to which components (or alternatively, which basic events) should receive more urgent attention in achieving system reliability growth. The new measure of component importance has certain desirable properties not possessed by the previous measure of component importance proposed by Birnbaum [6]. The measure is extended to minimal cut sets and to systems of components undergoing repair. A number of commonly occurring systems are treated in detail for illustrative purposes.