Study concept and design: Hipgrave, Chang, Li, Wu.
Acquisition, analysis, or interpretation of data: Hipgrave, Chang, Li, Wu.
Drafting of the manuscript: Hipgrave, Li.
Critical revision of the manuscript for important intellectual content: Hipgrave, Chang, Li, Wu.
Statistical analysis: Hipgrave, Chang, Li.
Obtained funding: Wu.
Administrative, technical, or material support: Hipgrave, Chang, Li, Wu.
Study supervision: Wu.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
Funding/Support: This work was supported by the National Natural Science Foundation of China (grant 21537001; 2007 and 2009 surveys), the National Basic Research Program of China (973 Program 2012CB720804; 2009 survey), the China Ministry of Health (grant 200902009; 2009 survey), and UNICEF (2009 survey). The authors were entirely funded by their institutions.
Role of the Funder/Sponsor: UNICEF played a role in the design and conduct of the study, collection, management, analysis and interpretation of the data, preparation, review and approval of the manuscript, and the decision to submit the manuscript for publication.