We are indebt to Huijuan Zhao, Ran Bian, Yun Xie, Baoguo Xie, Zhichao Wang, Yu Yan, and Yi Wu for administering the survey and preparing the data for the present study. We thank Huijuan Zhao, Ran Bian, and Xiao Li for translating the PGI from English into Chinese. We are grateful to Ms. Yuebin Jin who provided access to the high schools. Finally the cooperation of the students and schools where the data were collected is appreciated. This study was financially supported by Natural Science Foundation of China, Grant No. 70171046.