Online panel research a data quality perspective / editors by Mario Callegaro, Survey Research Scientist, Quantitative Marketing Team, Google UK, Reg Baker, Senior Consultant, Market Strategies International, USA, Jelke Bethlehem, Anja S. Goritz, Professor of Occupational and Consumer Psychology, University of Freiburg, Germany, Jon A. Krosnick, Professor of Political Science, Communication and Psychology, Stanford University, USA, Paul J. Lavrakas, Independent Research Psychologist