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Overview of reviews in child health: evidence synthesis and the knowledge base for a specific population.

BACKGROUND
Overviews of reviews are an evolving form of evidence synthesis. The Cochrane Child Health Field has been producing overviews since 2006, during which time the methods that have been used have changed, both due to the development of guidance within The Cochrane Collaboration and to the decisions made by individual author teams. This paper studies the first 29 overviews published in EBCH.


OBJECTIVES
To describe some aspects of the approaches taken in EBCH overviews to producing evidence syntheses relevant to the healthcare needs of children; to highlight the contribution that overviews can make to the knowledge base for treatment for a particular population.


METHODS
Data was extracted on: whether the overview included systematic review (SR) data only, or also data from individual trials not present in the included SRs; name(s) of the Cochrane Review Group (CRG) that prepared the included SRs; topics of the overviews as compared to the topics of the included reviews; age-subgroup analyses presented in the overviews.


RESULTS
In 23 overviews, all published in 2012, the authors included trial data as well as SR data; two overviews addressed conditions not explicitly addressed by the included reviews; three overviews included pre-specified age-subgroup analyses.


DISCUSSION
The aim of clinical relevance has been achieved by means such as: drawing from reviews produced by multiple CRGs; using SR evidence to explore clinically relevant topics that may not match exactly with the topics covered by the SRs; ensuring that the evidence in overviews is as up to date as possible by redoing searches and including trials not incorporated in the included SRs; and, where permitted by the data, using age-subgroup analyses to present the data in a way which matches the stages of childhood development.


CONCLUSION
Overview authors are dependent on the nature of the data and methods reported in the included SRs. This suggests a need for further study about how SRs could be conducted in order to facilitate the conduct of overviews.