[1] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Int Hlth, Baltimore, MD 21205 USA
[2] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Populat Family & Reprod Hlth, Baltimore, MD 21205 USA
[3] Univ Montreal, Dept Demog, Quebec City, PQ, Canada
[4] Johns Hopkins Bloomberg Sch Publ Hlth, Bill & Melinda Gates Inst Populat & Reprod Hlth, Baltimore, MD 21205 USA