Evidence synthesis is the process of retrieving, evaluating, combining and summarising the findings of all relevant studies on a certain subject area. Ideally, a systematic review is conducted to identify all the relevant available studies to support the evidence synthesis.
For more information about systematic reviewing, see the Cochrane Handbook for Systematic Reviews of Interventions.
For guidance on conducting a systematic literature review in the context of exploring and identifying drivers of effectiveness, see Conducting a Literature Review.
Meta-analyses may be used to combine the estimates from the individual studies identified in the systematic review.
Network meta-analysis (NMA) is an extension of standard, pairwise meta-analysis, which can be used to synthesise results from studies that compare different sets of alternative interventions for the same condition. NMA is a form of indirect comparison, and it is particularly useful if there are no head-to-head trials comparing a new intervention with the comparator of interest (e.g. usual care).
For more information about evidence synthesis and network meta-analysis, see Overview of Evidence Synthesis and Network Meta-Analysis.
Including RWD in evidence synthesis
Meta-analysis and NMA have traditionally been limited to combining the results of randomised controlled trials (RCTs), because such trials are considered to be the most reliable source of information on relative treatment effects. However, there is a growing interest in incorporating evidence from non-randomised studies (NRSs), patient registries and other real-world data (RWD) in these analyses.
This strategy is particularly appealing when there are few RCTs to answer a specific research question. It may also be useful when the available RCTs do not align with the target population, prescription strategies and/or primary outcomes of the research question (i.e. when there is an Efficacy-Effectiveness gap).
Including RWD may be also be helpful to connect disconnected networks of interventions (i.e. if trials comparing interventions are not available) or to supplement existing RCT evidence when the results are conflicting or evidence is limited.
For more information about incorporating RWD into an NMA, see Network Meta-Analysis Incorporating RWE.