Københavns Universitet - Økonomisk Institut - Publikationer (DK) *

  1. How McFadden Met Rockafellar and Learnt to Do More With Less

    Sørensen, Jesper Riis-Vestergaard & Fosgerau, Mogens, 30 apr. 2020, I : SSRN Electronic Journal.

    Publikation:Bidrag til tidsskriftTidsskriftartikelForskning

    We study the additive random utility model of discrete choice under minimal assumptions. We make no assumptions regarding the distribution of random utility components or the functional form of systematic utility components. Exploiting the power of convex analysis, we are nevertheless able to generalize a range of important results. We characterize demand with a generalized Williams-Daly-Zachary theorem. A similarly generalized version of Hotz-Miller inversion yields constructive partial identification of systematic utilities. Estimators based on our partial identification result remain well defined in the presence of zeros in demand. We also provide necessary and sufficient conditions for point identification.
    TidsskriftSSRN Electronic Journal
    StatusUdgivet -30 apr. 2020
  2. Functional and Biomechanical Performance of Stentless Extracellular Matrix Tricuspid Tube Graft: An Acute Experimental Porcine Evaluation

    Ropcke, D. M., Ilkjær, C., Skov, Søren, Tjørnild, M. J., Sørensen, A. V., Jensen, Henrik, Jensen, M. O. J., Hjortdal, Vibeke Elisabeth & Nielsen, S. L., jan. 2016, I : The Annals of Thoracic Surgery. 101, 1, s. 125-32 8 s.

    Publikation:Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

    BACKGROUND: Stentless porcine extracellular matrix tricuspid tubular valves have been developed for tricuspid valve reconstruction. The purpose of this study was to compare biomechanical and functional performance of native and tube graft valves in an acute porcine model.

    METHODS: Twenty-two 65-kg pigs were randomized to tube graft or control with native valve preservation. Anterior papillary muscle force was measured with a dedicated force transducer. Microtip pressure catheters were placed in the right atrium and ventricle. Leaflet motion and three-dimensional valve geometry were evaluated using 13 sonomicrometry crystals: six in the tricuspid annulus, one on each leaflet free edge, one on each papillary muscle tip, and one in the right ventricular apex.

    RESULTS: No regurgitation and no significant differences in intracavitary pressures, annular motion, or leaflet excursion angles were observed after tube graft implantation (p > 0.05). Compared with the native valve, the tricuspid annulus, leaflet orifice area, annular diameters, and the septal segment of the annulus were significantly smaller in the tube graft group (p < 0.05). Maximum anterior papillary muscle force was significantly lower in the tube graft group (p < 0.005). The implantation technique led to an annular circumferential downsizing of 20% ± 17%.

    CONCLUSIONS: An extracellular matrix tube graft implanted in the tricuspid position produces a competent valve with physiologic performance that, despite downsizing, makes the tube graft an attractive alternative to valve replacement. The downsizing of the implantation should be considered when planning tube graft size and may be potentially beneficial by relieving tension on the repaired tissue, thereby increasing durability.

    TidsskriftThe Annals of Thoracic Surgery
    Udgave nummer1
    Sider (fra-til)125-32
    Antal sider8
    StatusUdgivet -jan. 2016

    Bibliografisk note

    Copyright © 2016 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

  3. Graph Refinement based Airway Extraction using Mean-Field Networks and Graph Neural Networks

    Selvan, Raghav, Kipf, T., Welling, M., Juarez, A. G., Pedersen, J. H., Petersen, Jens & de Bruijne, Marleen, 2 jun. 2020, I : Medical Image Analysis.

    Publikation:Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

    Graph refinement, or the task of obtaining subgraphs of interest from over-complete graphs, can have many varied applications. In this work, we extract trees or collection of sub-trees from image data by, first deriving a graph-based representation of the volumetric data and then, posing the tree extraction as a graph refinement task. We present two methods to perform graph refinement. First, we use mean-field approximation (MFA) to approximate the posterior density over the subgraphs from which the optimal subgraph of interest can be estimated. Mean field networks (MFNs) are used for inference based on the interpretation that iterations of MFA can be seen as feed-forward operations in a neural network. This allows us to learn the model parameters using gradient descent. Second, we present a supervised learning approach using graph neural networks (GNNs) which can be seen as generalisations of MFNs. Subgraphs are obtained by training a GNN-based graph refinement model to directly predict edge probabilities. We discuss connections between the two classes of methods and compare them for the task of extracting airways from 3D, low-dose, chest CT data. We show that both the MFN and GNN models show significant improvement when compared to one baseline method, that is similar to a top performing method in the EXACT'09 Challenge, and a 3D U-Net based airway segmentation model, in detecting more branches with fewer false positives.
    TidsskriftMedical Image Analysis
    StatusUdgivet -2 jun. 2020
  4. The Greek crisis: a story of self-reinforcing feedback mechanisms

    Juselius, Katarina & Dimelis, S., 4 feb. 2019, I : Economics. 13, s. 1-23

    Publikation:Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

    While there seems to be a well-established consensus about the underlying causes to the Greek crisis, less is known about internal and external transmission mechanisms that ultimately caused unemployment to increase rapidly over this period. Motivated by the structural slumps theory in Phelps (Structural slumps, 1994), the paper attempts, therefore, to uncover the dynamic mechanisms behind prices, interest rates, and external imbalances that contributed to the severity and the length of the crisis. The authors find that the strongly increasing real bond rate and unemployment rate together with an persistently appreciating real exchange rate and a deterioration of competitiveness in the eurozone have contributed to persistently growing structural imbalances in the Greek economy. As the lack of confidence in the Greek economy grew steadily, the scene was set for a monumental structural slump. Over the crisis period, all variables exhibited self-reinforcing feedback adjustment somewhere in the system except for inflation rate. Unemployment took the burden of adjustment when the bond rate sky rocketed, competitiveness deteriorated, and confidence fell.
    Sider (fra-til)1-23
    StatusUdgivet -4 feb. 2019
  5. The effect of assigning dedicated general practitioners to nursing homes

    Weatherall, C. D., Hansen, A. T. & Nicholson, S., 17 jan. 2019, I : Health Services Research. 54, 3, s. 547-554

    Publikation:Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

    To determine whether assigning a dedicated general practitioner (GP ) to a nursing home reduces hospitalizations and readmissions.

    Data Sources/Study Setting
    Secondary data on hospitalizations and deaths by month for the universe of nursing home residents in Denmark from January 2011 through February 2014.

    Study Design
    In 2012, Denmark initiated a program in seven nursing homes that volunteered to participate. We used a difference‐in‐differences model to estimate the effect of assigning a dedicated GP to a nursing home on the likelihood that a nursing home resident will be hospitalized, will experience a preventable hospitalization, and will be readmitted. The unit of observation is a resident‐month.

    Data Collection/Extraction Methods
    Data were extracted from the Danish public administrative register dataset.

    Principal Findings
    We found that assigning a GP to a nursing home was associated with a 0.55 [95 percent CI , 0.08 to 1.02] percentage point reduction in the monthly probability of a preventable hospitalization, which was a 26 percent reduction from the preintervention level of 2.13 percentage points. The associated reduction in the monthly probability of a readmission was 0.68 [95 percent CI , −0.01 to 1.37] percentage points, which was a 25 percent reduction from the baseline level of 2.68 percentage points. Survey results indicated that the likely mechanism for the effect was more efficient and consistent communication between GP s and nursing home personnel.

    Assigning a dedicated physician in a nursing home can reduce medical spending and improve patients' health.
    TidsskriftHealth Services Research
    Udgave nummer3
    Sider (fra-til)547-554
    StatusUdgivet -17 jan. 2019