1. is Research Professor, Department of Maternal and Child Health and Faculty Fellow, Carolina Population Center University of North Carolina at Chapel Hill 123 W. Franklin St. Chapel Hill NC 27516 USA
2. is Boshamer Distinguished Professor, Department of Economics and Faculty Fellow, Carolina Population Center University of North Carolina at Chapel Hill 123 W. Franklin St. Chapel Hill NC 27516 USA
3. are Research Associates, Carolina Population Center University of North Carolina at Chapel Hill 123 W. Franklin St. Chapel Hill NC 27516 USA