Statistical identification of major event days: an application to continuity of supply regulation in Italy

The Italian regulatory mechanism for quality of service in electricity distribution links the tariff to the SAIDI indicator of the average duration of interruptions per consumer. In order to separate major interruption events data from normal operation data, the regulator introduced, in the year 2000, a criterion based on a given definition of force majeure . For the new regulatory period, beginning in 2004, the authors studied the possibility of substituting this criterion with one based on a statistical definition of major event days. The statistical two-step methodology illustrated here was tested using real data and proposed to interested parties in the consultation process; it was found to be at the same time equitable, unambiguous, and simple to implement. This criterion was thus adopted in the new regulatory framework.