Measures of component importance in reliability theory

In this paper we survey the literature concerning the topic of measures of importance for components in binary coherent systems. The diverse measures discussed fall into one of the following three broad categories: structural measures, time dependent measures and time independent measures. Comparisons are made between various measures, and a framework for possible new measures is suggested. More research is needed in assessing the quantitative and qualitative properties of each of these measures as well as their interrelationships, and it is suggested that the most appropriate measure for a given situation is often highly dependent on the type of improvement for a system that is being envisaged.