Acknowledgments
Ming-Liang Zhang, Fang-Zhou Liu and Xiao-Long Chen conducted the literature search and study selection, performed data extraction and evaluated study quality. Wei-Xia Li, Xiao-Yan Wang and Hui Zhang verified quality assessments. Pan-Pan Chen and Wen-Hui Jia performed the quantitative meta-analyses and drafted the manuscript with contributions from the other authors. Lu Niu and Yan Wang helped in the interpretation of results. Jin-Fa Tang was responsible for the project and participated in its implementation. All authors read and approved the final manuscript.