1. Department of Statistics, George Mason University , 4400 University Drive, Fairfax, VA 22030 , USA
2. Institute for Social Research, University of Michigan-Ann Arbor , 426 Thompson Street, Ann Arbor, MI 48106 , USA
3. Department of Biostatistics and Bioinformatics, George Washington University , 800 22nd Street, NW, Washington, DC 20052 , USA
4. Center for Statistical Research and Methodology, U.S. Census Bureau , 4600 Silver Hill Rd, Suitland, MD 20746 , USA