The method used to conduct this systematic review has been previously registered in PROSPERO, an international database of prospectively registered systematic reviews, (CRD42016045832) which is available from http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42016045832. This systematic review was conducted in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines.