1. Department of Sociology and Institute for Empirical Social Science Research, School of Humanities and Social Science Xi'an China
2. Department of Sociology & Centre on Migration and Mobility, The Chinese University of Hong Kong, and Institute for Population and Development StudiesXi'an Jiaotong University Xi'an China
3. Institute for Population and Development StudiesXi'an Jiaotong University Xi'an China
4. Morrison Institute for Population and Resource StudiesStanford University California