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    <title>EconStor Community: Universität zu Köln</title>
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  <item rdf:about="http://hdl.handle.net/10419/73684">
    <title>A Jarque-Bera test for sphericity of a large-dimensional covariance matrix</title>
    <link>http://hdl.handle.net/10419/73684</link>
    <description>Title: A Jarque-Bera test for sphericity of a large-dimensional covariance matrix
&lt;br/&gt;
&lt;br/&gt;Authors: Glombek, Konstantin
&lt;br/&gt;
&lt;br/&gt;Abstract: This article provides a new test for sphericity of the covariance matrix of a d-dimensional multinormal population X ∼ Nd(µ,Σ). This test is applicable if the sample size, n + 1, and d both go to infinity while d/n → y ∈ (0,∞), provided that the limits of tr(Σk)/d, k = 1,...,8, are finite. The main idea of this test is to check whether the empirical eigenvalue distribution of a suitably standardized sample covariance matrix obeys the semicircle law. Due to similarities of the semicircle law to the normal distribution, the proposed test statistic is of the type of the Jarque-Bera test statistic. Simulation results show that the new sphericity test outperforms the tests from the current literature for certain local alternatives if y is small.</description>
  </item>
  <item rdf:about="http://hdl.handle.net/10419/73684">
    <title>A Jarque-Bera test for sphericity of a large-dimensional covariance matrix</title>
    <link>http://hdl.handle.net/10419/73684</link>
    <description>Title: A Jarque-Bera test for sphericity of a large-dimensional covariance matrix
&lt;br/&gt;
&lt;br/&gt;Authors: Glombek, Konstantin
&lt;br/&gt;
&lt;br/&gt;Abstract: This article provides a new test for sphericity of the covariance matrix of a d-dimensional multinormal population X ∼ Nd(µ,Σ). This test is applicable if the sample size, n + 1, and d both go to infinity while d/n → y ∈ (0,∞), provided that the limits of tr(Σk)/d, k = 1,...,8, are finite. The main idea of this test is to check whether the empirical eigenvalue distribution of a suitably standardized sample covariance matrix obeys the semicircle law. Due to similarities of the semicircle law to the normal distribution, the proposed test statistic is of the type of the Jarque-Bera test statistic. Simulation results show that the new sphericity test outperforms the tests from the current literature for certain local alternatives if y is small.</description>
  </item>
  <item rdf:about="http://hdl.handle.net/10419/71886">
    <title>Efficiency effects of quality of service and environmental factors: Experience from Norwegian electricity distribution</title>
    <link>http://hdl.handle.net/10419/71886</link>
    <description>Title: Efficiency effects of quality of service and environmental factors: Experience from Norwegian electricity distribution
&lt;br/&gt;
&lt;br/&gt;Authors: Growitsch, Christian; Jamasb, Tooraj; Wetzel, Heike
&lt;br/&gt;
&lt;br/&gt;Abstract: Since the 1990s, efficiency and benchmarking analysis has increasingly been used in network utilities research and regulation. A recurrent concern is the effect of environmental factors that are beyond the influence of firms (observable heterogeneity) and factors that are not identifiable (unobserved heterogeneity) on measured cost and quality performance of firms. This paper analyses the effect of geographic and weather factors and unobserved heterogeneity on a set of 128 Norwegian electricity distribution utilities for the 2001-2004 period. We utilize data on almost 100 geographic and weather variables to identify real economic inefficiency while controlling for observable and unobserved heterogeneity. We use the factor analysis technique to reduce the number of environmental factors into few composite variables and to avoid the problem of multicollinearity. We then estimate the established stochastic frontier models of Battese and Coelli (1992; 1995) and the recent true fixed effects models of Greene (2004; 2005) without and with environmental variables. In the former models some composite environmental variables have a significant effect on the performance of utilities. These effects vanish in the true fixed effects models. However, the latter models capture the entire unobserved heterogeneity and therefore show significantly higher average efficiency scores.</description>
  </item>
  <item rdf:about="http://hdl.handle.net/10419/71885">
    <title>Civil unrest in North Africa: Risks for natural gas supply?</title>
    <link>http://hdl.handle.net/10419/71885</link>
    <description>Title: Civil unrest in North Africa: Risks for natural gas supply?
&lt;br/&gt;
&lt;br/&gt;Authors: Lochner, Stefan; Dieckhöner, Caroline
&lt;br/&gt;
&lt;br/&gt;Abstract: The uprising and military confrontation in Libya that began in February 2011 has led to disruptions of gas supplies to Europe. An analysis of how Europe has compensated for these missing gas volumes shows that this situation has not affected security of supply. However, this situation would change if the North African uprising were to spread to Algeria. Since Algeria is a much more important gas supplier to Europe than is Libya, more severe consequences would be likely. Applying a natural gas infrastructure model, we investigate the impact of supplier disruptions from both countries for a summer and winter period. Our analysis shows that disruptions in the low-demand summer months could be compensated for, mainly by LNG imports. An investigation of a similar situation at the beginning of the winter shows that security of supply would be severely compromised and that disruptions to Italian consumers would be unavoidable.</description>
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