1. Mannheim Center for European Social Research (MZES), University of Mannheim, 68159 Mannheim, Germany
2. Cline Center for Advanced Social Research, University of Illinois, Urbana-Champaign, IL 61870-7461, USA
3. Department of Media and Communication, Ludwig-Maximilians-University, 80538 Munich, Germany
4. Department of Communication Sciences, Free University of Amsterdam, 1081 HV Amsterdam, the Netherlands