1. University of Erfurt, Nordhäuser Straße 63, 99089 Erfurt, Germany, and Max Planck Institute for Research on Collective Goods, Bonn (email: )
2. Technische Hochschule Nürnberg Georg Simon Ohm, Faculty of Business Administration, Bahnhofstrasse 87, 90402 Nürnberg, Germany (email: )
3. Technical University of Kaiserslautern (TUK), Gottlieb-Daimler-Straße, 67663 Kaiserslautern, Germany (email: )