About the Authors

Neff Walker, Fengmin Zhao
Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, United States of America

Kenneth Hill
Harvard School of Public Health, Harvard University, Cambridge, Massachusetts, United States of America

Corresponding Author

kenneth_hill_1@yahoo.com

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Wrote the first draft of the manuscript: KH NW. Contributed to the writing of the manuscript: KH NW. ICMJE criteria for authorship read and met: NW KH FZ. Agree with manuscript results and conclusions: NW KH FZ. Conceived the analysis: NW. Collaborated on design of the analysis: KH. Performed the analysis: KH FZ. Analyzed the results: NW KH.