1. A network management system for identifying and accessing Quality of Service, QoS, issues within a communications network, the network management system comprising: a service performance database that stores a plurality of service performance records; a factor score database that stores a plurality of computed factor scores for each service performance record together with a reference to the corresponding service performance record; and at least one processor comprising: a service performance unit, coupled to the service performance database, that (1) captures traffic, and performance related data on interfaces in the communications network and at nodes in the communications network, (2) format the captured traffic and performance related data into service usage transactions each including an identification field and a factor, where the factor describes an aspect of the communications network when the corresponding service usage transaction has taken place, and (3) correlate the individual service usage transactions based on the identification fields to create the plurality of service performance records each including one of the identification fields, multiple factors, and a service quality metric; a factor scoring system, coupled to the service performance database, that computes a factor score for each factor in each service performance record, where the factor score indicates an influence the corresponding factor has on the corresponding service quality metric, wherein the factor scoring system is adapted to compute the factor score for each factor by: computing an empirical distribution of a selected one of the service quality metrics for all of the service performance records; computing an empirical distribution of the one service quality metric for the subset of the service performance records having a similar factor value for a selected one factor; and computing the factor score as a function of the computed empirical distribution of the selected one of the service quality metrics for all of the service performance records and the computed empirical distribution of the one service quality metric for the subset of the service performance records having the similar factor value for the selected one factor; and a factor strength analysis module, coupled to the factor score database and the service performance database, that aggregates at least a subset of the service performance records together with the corresponding factor scores and uses a rule set to analyze the aggregated records to indicate a cause for a specific service quality degradation detected within the communications network.