Author contributions
Study concept and design: Qiao Y, and Niu GD. Analysis and
interpretation of data: Qiao Y, Zhao Z, Fu MP, Cai X, Guo YL, Liu K, and
Guo JR. Drafting of the manuscript: Qiao Y and Niu GD. Critical revision
of the manuscript for important intellectual content: Qiao Y, Guo T, and
Niu GD. Statistical analysis: Qiao Y. Approval of the article: Qiao Y,
Zhao Z, Fu MP, Cai X, Guo YL, Liu K, Guo JR, Guo T, and Niu GD.