1. Survey Methodologist at Westat, 1600 Research Blvd., Rockville, MD 20850, USA
2. Research Professor at the Survey Research Center, Institute for Social Research, University of Michigan, 426 Thompson Street, Ann Arbor, MI 48104, USA and at the Joint Program in Survey Methodology, University of Maryland
3. Professor, Director at the Joint Program in Survey Methodology (JPSM), University of Maryland, 1218 LeFrak Hall, College Park, MD 20742, USA
4. Professor of Statistics and Methodology at the University of Mannheim, 68131 Mannheim, Germany