作者单位:Demography and Social Statistics, Obafemi Awolowo University, Ile-Ife, Nigeria,[1]Mailman School of Public Health, Columbia University, 60 Haven Avenue, New York, NY 10032, United[2]Operations Research Unit, Kano, Nigeria[3]Demography and Social Statistics, Obafemi Awolowo University, Ile-Ife, Nigeria[4]