Studying the performance of a distributed system without taking care on the impact of its management system will falsify the understanding of its overall performance, especially its productivity. We propose a metric called MIM (Management Impact Metric) to evaluate this impact by varying one or several impact factors related to the management system within a management strategy of the managed system. We show the accuracy and interest of our metric on a managed J2EE application server that uses a management architecture based on the JMX standard.