@article{NeumannNieswandSchubert2016,
  author    = {Neumann, Anne and Nieswand, Maria and Schubert, Torben},
  title     = {Estimating alternative technology sets in nonparametric efficiency analysis: restriction tests for panel and clustered data},
  series = {Journal of productivity analysis},
  volume    = {45},
  journal   = {Journal of productivity analysis},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {0895-562X},
  doi       = {10.1007/s11123-015-0461-z},
  pages     = {35 -- 51},
  year      = {2016},
  abstract  = {Nonparametric efficiency analysis has become a widely applied technique to support industrial bench-marking as well as a variety of incentive-based regulation policies. In practice such exercises are often plagued by incomplete knowledge about the correct specifications of inputs and outputs. Simar and Wilson (Commun Stat Simul Comput 30(1): 159-184, 2001) and Schubert and Simar (J Prod Anal 36(1): 55-69, 2011) propose restriction tests to support such specification decisions for cross-section data. However, the typical oligopolized market structure pertinent to regulation contexts often leads to low numbers of cross-section observations, rendering reliable estimation based on these tests practically unfeasible. This small-sample problem could often be avoided with the use of panel data, which would in any case require an extension of the cross-section restriction tests to handle panel data. In this paper we derive these tests. We prove the consistency of the proposed method and apply it to a sample of US natural gas transmission companies from 2003 through 2007. We find that the total quantity of natural gas delivered and natural gas delivered in peak periods measure essentially the same output. Therefore only one needs to be included. We also show that the length of mains as a measure of transportation service is non-redundant and therefore must be included.},
  language  = {en}
}
@article{ZaklanAbrellNeumann2016,
  author    = {Zaklan, Aleksandar and Abrell, Jan and Neumann, Anne},
  title     = {Stationarity changes in long-run energy commodity prices},
  series = {Energy economics},
  volume    = {59},
  journal   = {Energy economics},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0140-9883},
  doi       = {10.1016/j.eneco.2016.07.022},
  pages     = {96 -- 103},
  year      = {2016},
  abstract  = {Situated at the intersection of the literatures on speculative storage and non-renewable commodity scarcity, this paper considers whether changes in persistence have occurred in long-run U.S. prices of the energy commodities crude oil, natural gas and bituminous coal. We allow for a structural break when testing for a break in persistence to avoid a change in the stochastic properties of prices being confounded by an unaccounted-for deterministic shift in the price series. We find that coal prices are trend stationary throughout their evolution and that oil prices change from stationarity to non-stationarity in the decade between the late 1960s to late 1970s. The result on gas prices is ambiguous. Our results demonstrate the importance of accounting for a possible structural shift when testing for breaks in persistence, while being robust to the exact date of the structural break. Based on our analysis we caution against viewing long-run energy commodity prices as being non-stationary and conclude in favor of modeling commodity market fundamentals as stationary, meaning that speculative storage will tend to have a dampening effect on prices. We also cannot reject that long-run prices of coal and, with some hesitation, gas follow a Hotelling-type rule. In contrast, we reject the Hotelling rule for oil prices since the late 1960s/early 1970s. (C) 2016 Elsevier B.V. All rights reserved.},
  language  = {en}
}