As part of RIIO-ED1, the first electricity distribution price control review under the RIIO model, Ofgem had stated that, unless there was a strong rationale for adopting other approaches to assess distribution network operators’ total expenditure, it intended to use a relatively simple econometric modelling approach(es) to assess their relative efficiency levels. Oxera, in association with Oxera Associate, Distinguished Professor Subal Kumbhakar, examined alternative efficiency modelling approaches developed by Professor Kumbhakar and other academics over the last 40 years. This was the first known application of such approaches in the sector. Oxera’s assessment demonstrated, both theoretically and empirically, that these alternative approaches could validly be applied to DNO data, with the empirical analysis confirming the theoretical foundations of the models. In addition, models that can robustly control for company-specific effects and noise in the cost assessment exercise can provide more robust estimates of the DNOs’ relative efficiency levels, and therefore could improve the accuracy of the efficiency analysis and lessen the need for ad hoc assumptions and regulatory judgement.