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Table 3 Definitions

From: What guidance is available for researchers conducting overviews of reviews of healthcare interventions? A scoping review and qualitative metasummary

Indirect comparison: “A comparison of two interventions via one or more common comparators. For example, the combination of intervention effects from AC and intervention effects from BC studies may (in some situations) be used to learn about the intervention effect AB.” (http://methods.cochrane.org/cmi/node/61)  
Network meta-analysis: “An analysis that syntheses information over a network of comparisons to assess the comparative effects of more than two alternative interventions for the same condition. A network meta-analysis synthesizes direct and indirect evidence over the entire network, so that estimates of intervention effect are based on all available evidence for that comparisons. This evidence may be direct evidence, indirect evidence or mixed evidence. Typical outputs of a network meta-analysis are a) relative intervention effects for all comparisons; and b) a ranking of the interventions.” (http://methods.cochrane.org/cmi/node/61)  
Non-Cochrane systematic reviews: Systematic reviews published outside of the Cochrane Database of Systematic Reviews.  
Overlapping systematic reviews: Two or more systematic reviews examining the same intervention for the same disorder. Overlapping systematic reviews will often contain one or more of the same primary studies, which may lead to including the same study’s outcome data in an overview two or more times.  
Quality of evidence: The confidence we have in the outcome effect estimates, often assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) tool.  
Transitivity assumption: “The situation in which an intervention effect measured using an indirect comparison is valid and equivalent to the intervention effect measured using a direct comparison. Specifically, the transitivity assumption states that (the benefit of A over B) is equal to (the benefit of A over C) plus (the benefit of C over B). Equivalently, this may be written as (the benefit of A over C) minus (the benefit of B over C). In practice, transitivity requires similarity; that is that the sets of studies used to obtain the indirect comparison are sufficiently similar in characteristics that moderate the intervention effect. Transitivity can be thought of as a network meta-analysis extension of the idea of homogeneity in a standard meta-analysis.” (http://methods.cochrane.org/cmi/node/61)