Resources (10, 20, 30) of a communications network (40), are used to provide services, some are superordinate services (A, B) which depend on contributory services (C, D, E, F). Key performance indicators R-KPI are received based on measurements from the resources, of contributory services contributing to a corresponding key performance indicator KPI of the corresponding superordinate service. A selection (120) is made of the received R-KPIs which correspond to the normal operation of the superordinate service and a characteristic division is generated (130) of relative contributions of the R-KPIs to the KPI of the corresponding superordinate service for the times that the service was operating normally. This can be used as a basis for identifying differences with other R-KPIs to determine anomalies in behavior of contributory services for root cause analysis or in managing the network. Convergence evaluation and validation can be used to improve accuracy of the characteristic division.