1. A management method for a computer system comprising a node apparatus serving as an object to be monitored and a management system which is coupled to the node apparatus over a network and monitors and manages the node apparatus, comprising: acquiring a processing performance value indicating processing performance of the node apparatus and sensing a status of the node apparatus from the acquired processing performance value, by the management system; applying the sensed status to an analysis rule indicating a relationship between a combination of one or more condition events which may occur in the node apparatus and a conclusion event which is presumed to be a root cause of the combination of the condition events and calculating a certainty factor which is information indicating possibility of occurrence of a failure in the node apparatus, by the management system; determining, from the certainty factor, whether a failure has occurred in the node apparatus, by the management system; displaying an unresolved failure analysis result which is a failure analysis result for the node apparatus when the status remains abnormal and a resolved failure analysis result which is a failure analysis result for the node apparatus when the status has changed from abnormal to normal on a display screen without changing information on the certainty factor if it is determined that a failure has occurred in the node apparatus, by the management system.