University of Mannheim

About: University of Mannheim is a education organization based out in Mannheim, Germany. It is known for research contribution in the topics: Population & European union. The organization has 4448 authors who have published 12918 publications receiving 446557 citations. The organization is also known as: Uni Mannheim & UMA.

Combined SVM-Based Feature Selection and Classification

Abstract: Feature selection is an important combinatorial optimisation problem in the context of supervised pattern classification. This paper presents four novel continuous feature selection approaches directly minimising the classifier performance. In particular, we include linear and nonlinear Support Vector Machine classifiers. The key ideas of our approaches are additional regularisation and embedded nonlinear feature selection. To solve our optimisation problems, we apply difference of convex functions programming which is a general framework for non-convex continuous optimisation. Experiments with artificial data and with various real-world problems including organ classification in computed tomography scans demonstrate that our methods accomplish the desired feature selection and classification performance simultaneously.

Choice-Based Elicitation and Decomposition of Decision Weights for Gains and Losses Under Uncertainty

Abstract: This paper reports the results of an experimental parameter-free elicitation and decomposition of decision weights under uncertainty. Assuming cumulative prospect theory, utility functions were elicited for gains and losses at an individual level using the tradeoff method. Subsequently, decision weights were elicited through certainty equivalents of uncertain two-outcome prospects. Furthermore, decision weights were decomposed using observable choice instead of invoking other empirical primitives, as in previous experimental studies. The choice-based elicitation of decision weights allows for a quantitative study of their characteristics, and also allows, among other things, for the examination of the sign-dependence hypothesis for observed choice under uncertainty. Our results confirm concavity of the utility function in the gain domain and bounded subadditivity of decision weights and choice-based subjective probabilities. We also find evidence for sign dependence of decision weights.

Characteristic sets: Accurate cardinality estimation for RDF queries with multiple joins

Abstract: Accurate cardinality estimates are essential for a successful query optimization. This is not only true for relational DBMSs but also for RDF stores. An RDF database consists of a set of triples and, hence, can be seen as a relational database with a single table with three attributes. This makes RDF rather special in that queries typically contain many self joins. We show that relational DBMSs are not well-prepared to perform cardinality estimation in this context. Further, there are hardly any special cardinality estimation methods for RDF databases. To overcome this lack of appropriate cardinality estimation methods, we introduce characteristic sets together with new cardinality estimation methods based upon them. We then show experimentally that the new methods are-in the RDF context-highly superior to the estimation methods employed by commercial DBMSs and by the open-source RDF store RDF-3X.

Price Competition and Product Differentiation When Consumers Care for the Environment

Abstract: Increasing environmental awareness may affect the pleasure of consuming a good for which an environmental friendly substitute is available. When deciding to buy differentiated products, a compromise is sometimes made between preferred characteristics of the good and its environmental properties. In this paper we investigate the market implication of product differentiation when customers are concerned about environmental aspects of the good. We use the spacial duopoly model to determine how environmental concern affects prices, product characteristics and market shares of the competing firms. Our analysis is based on a two-stage game where at the first stage each firm chooses the characteristic of its product. At the second stage each firm chooses its price. The unique equilibrium prices and market shares are affected by consumer awareness of the environment and by the higher costs for producing those goods. As for the Nash equilibria in the characteristics we find three equilibria depending on the parameter constellation. In order to find out whether the market functions in an optimal way we determined the choice of environmental characteristics by a welfare maximizing authority. The result of this analysis is that characteristics differ under private decision making and social one. It can be shown, however, that it is possible to choose environmental policy instruments in order to stimulate private firms to produce the social optimal qualities.

Measuring the Quality of E-Banking Portals

Abstract: Purpose – In the internet economy, the business model of web portals has spread rapidly over the last few years. Despite this, there have been very few scholarly investigations into the services and characteristics that transform a web site into a portal as well as into the dimensions that determine the customer's evaluation of the portal's service quality.Design/methodology/approach – Based on an empirical study in the field of e‐banking, the authors validate a measurement model for the construct of web portal quality based on the following dimensions: security and trust, basic services quality, cross‐buying services quality, added value, transaction support and responsiveness.Findings – The identified dimensions can reasonably be classified into three service categories: core services, additional services, and problem‐solving services.Originality/value – The knowledge of these dimensions as major determinants of consumer's quality perception in the internet provides banks a promising starting point for ...