Contribution to authorship
YQY and CX screened abstracts, selected eligible papers, extracted data and wrote the first draft of the paper. SSH and MYS screened abstracts and selected eligible papers. HHL, LYH and QW performed the statistical analysis. CLW, YW, LX and XFL helped in the final selection of papers in case of disagreement and reviewed the manuscript critically. JHT, LG and LS designed the study and revised the manuscript.