1. Senior Mathematical Statistician at U.S . Census Bureau, 4600 Silver Hill Road, Washington, DC 20233, USA
2. School of Public Health, University of Michigan Research Professor at the Survey Research Center, Institute for Social Research, University of Michigan, 426 Thompson Street, Ann Arbor, MI 48109, USA and Professor at the Department of Biostatistics, , 1415 Washington Heights, Ann Arbor, MI 48109, USA