1. Department of Sociology, University of Colorado Boulder, Boulder, CO, USA
2. Population Program, Institute of Behavioral Science, University of Colorado, 483 UCB, Boulder, CO 80309-0483, USA
3. University of Colorado Population Center, Institute of Behavioral Science, University of Colorado Boulder, Boulder, CO, USA
4. Health and Society Program, Institute of Behavioral Science, University of Colorado Boulder, Boulder, CO, USA