Cochrane Overviews of Reviews (Overviews) use explicit and systematic methods to search for and identify multiple systematic reviews on a similar topic for the purpose of extracting and analyzing their results across important outcomes. Thus, the unit of searching, inclusion and data analysis is the systematic review rather than the primary study. Overviews can search for and include both Cochrane and non-Cochrane systematic reviews.
Overviews can present outcome data exactly as they appear in the included systematic reviews, or they can re-analyze the outcome data. However, we recommend against undertaking network meta-analyses in the context of an Overview because the types of analysis and inference can be drawn are very different when study-level data are not sought.
The table below presents the differences between an Overview and a standard intervention review when addressing multiple interventions for the same condition.
Cochrane intervention review with network meta-analysis
Collate multiple systematic reviews about the effectiveness of interventions for the same condition to extract and analyse their results across important outcomes. Overviews may also be used for other purposes (see Handbook chapter).
Re-analyse data from randomized trials of multiple interventions for the same condition to make inferences about their comparative effectiveness or safety
Focus of search strategy
Primary studies such as individual randomized trials
Focus of statistical synthesis
Focus of data collection
Summary estimates based on existing meta-analyses from the included reviews
Estimates from primary studies