Abstract
This paper measures TFP growth of Telefonica del Peru, and based on this growth rate computes a telecommunications X-factor or offset. More broadly the paper analyses the problem of updating an X-factor under existing price cap regulation. A revised offset must account for the possible restructuring of service offerings resulting from improved efficiencies in response to price cap incentives. Our updating framework focuses on efficiency criteria, and based on economic principles emphasizes the continuity between prior and continuing standards. In the case of Peru, based on annual average TFP growth of 1.66%, the X-factor is computed to be 4.06% per year.