About the Authors
Population Studies Center, University of Pennsylvania, Philadelphia, Pennsylvania, United State of America
United Nations Population Division, New York, New York, United States of America
The authors have declared that no competing interests exist. The views expressed in this paper are those of the authors and do not necessarily reflect the views of the United Nations. Its contents have not been formally edited and cleared by the United Nations.
Analyzed the data: MG PG FP AS. Wrote the first draft of the manuscript: MG. Contributed to the writing of the manuscript: MG PG FP. ICMJE criteria for authorship read and met: MG PG FP AS. Agree with manuscript results and conclusions: MG PG FP AS.