Comparison results for inactivity times of k-out-of-n and general coherent systems with dependent components

Coherent systems, i.e., multicomponent systems where every component monotonically affects the working state or failure of the whole system, are among the main objects of study in reliability analysis. Consider a coherent system with possibly dependent components having lifetime T, and assume we know that it failed before a given time $$t>0$$ t > 0 . Its inactivity time $$t-T$$ t - T can be evaluated under different conditional events. In fact, one might just know that the system has failed and then consider the inactivity time $$(t-T|T\le t)$$ ( t - T | T ≤ t ) , or one may also know which ones of the components have failed before time t, and then consider the corresponding system’s inactivity time under this condition. For all these cases, we obtain a representation of the reliability function of system inactivity time based on the recently defined notion of distortion functions. Making use of these representations, new stochastic comparison results for inactivity times of systems under the different conditional events are provided. These results can also be applied to order statistics which can be seen as particular cases of coherent systems (k-out-of-n systems, i.e., systems which work when at least k of their n components work).