About the Authors
- Qingyue Meng
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* E-mail: qmeng@bjmu.edu.cn
Affiliation China Center for Health Development Studies, Peking University, Beijing, China
- Ling Xu
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Affiliation Center for Health Statistics and Information, China National Health and Family Planning Commission, Beijing, China
Competing Interests
The authors have declared that no competing interests exist.
Author Contributions
Analyzed the data: QM LX. Wrote the first draft of the manuscript: QM LX. Contributed to the writing of the manuscript: QM LX. ICMJE criteria for authorship read and met: QM LX. Agree with manuscript results and conclusions: QM LX.