AUTHOR CONTRIBUTIONS
Bo Zheng and Jian Wang designed the study. Yan Li and Yang Fan conducted statistical analyses. Gangfeng Gu, Yan Li, Jian Yang, Junyao Jiang, Zhao Chen, Yang Fan and Sheng Wang contributed to data collection. Bo Zheng and Yan Li wrote the paper. Bo Zheng, Han Pei and Jian Wang revised the manuscript. All authors approved the final draft.