2.4 Quality assessment and data extraction
The study quality was evaluated by two investigators (L-MF and L-MJ) using the Newcastle–Ottawa Scale (NOS) for observational studies and Delphi consensus criteria for randomized controlled study (RCTs). The NOS system consisted of eight questions with nine possible points. A star system was used to judge the data according to the selected populations and the comparability of the groups and exposure/outcome of interest. A study with NOS ≥7 was judged to be a study of good quality8. The Preferred Reporting Items for Systematic Reviews and Meta-analyses Amendment to the Quality of Reporting of Meta-analyses Statement and recommendations from the Cochrane Collaboration in epidemiology were followed while performing the present systematic review. Data extraction was conducted by mutual agreement, and all potential disagreements were solved by consensus 9, 10.