Abstract: A method of determining the level of the effect of each system entity on the overall system performance, wherein the status of each entity at each one of discrete points of time is determined as the corresponding one of an active and an inactive status; the length of the active period in which each entity is situated without interruption in the active status is determined as an active time; and, on the basis of the relationship in magnitude between the system entities with respect to the determined active time, the level at which each entity affects the performance of the system is determined.