date:Jun 11, 2015
The review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement and was registered in an international prospective register of systematic reviews. Meta-analysis consists of applying statistical methods for combining the findings from different independent but similar studies. Reviewers followed strict criteria for including or excluding studies and then pooled and tested the data for sources of agreement or disagreement.
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