1. ZEW-Leibniz Centre for European Economic Research , Mannheim, Baden-Württemberg, Germany . e-mail: bettina.peters@zew.de ; e-mail: martinhud@web.de ; e-mail: christian.koehler@rocketmail.com
2. Center for Innovation Systems and Policy, AIT Austrian Institute of Technology , Vienna, Austria . e-mail: bernhard.dachs@ait.ac.at