Meta-Analysis doi: 10.1136/bmj.m696. Affiliations Affiliations 1 Evidence Based Social Science Research Centre, School of Public Health, Lanzhou University, Lanzhou, China. 2 Department of Social Medicine and Health Management, School of Public Health, Lanzhou University, Lanzhou, China. 3 Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON, Canada. 4 Michael G DeGroote Institute for Pain Research and Care, McMaster University, Hamilton, ON, Canada.