Characterizing updated and living meta-analyses Part 1: A methodological scoping review on methods for conducting meta-analyses in updated and living systematic reviews.

Abstract

Systematic reviews (SRs) provide the highest level of evidence for clinical and policy decision-making but quickly become outdated as new studies emerge. Updated systematic reviews (USRs) and living systematic reviews (LSRs) offer two frameworks to maintain currency; however, statistical approaches for repeated updates of pairwise meta-analyses (PMA) and network meta-analyses (NMA) remain heterogeneous. This scoping review aimed to identify, categorize, and summarize existing methods for conducting updated meta-analyses (primarily PMAs and, subject to available evidence, NMAs) in the context of USRs and LSRs, highlighting their properties, as well as their reported advantages and limitations. A scoping review was conducted to identify studies that described or compared methods for updating PMAs or NMAs within USRs or LSRs. We followed the 2020 JBI methodology and searched across major bibliographic databases (MEDLINE, Embase, the Cochrane Library, Cochrane CENTRAL, the Cochrane Methodology Register, ERIC, and PsycINFO) from inception to March 6, 2024. Grey literature and expert recommendations supplemented our literature search. Two reviewers independently screened records, extracted data, and categorized methods. Of 2710 records identified, 51 studies and one companion report met inclusion criteria. The studies were grouped into nine methodological categories: Traditional/Cumulative Meta-analysis, Law of Iterated Logarithm, Shuster Sequential Method, Sequential Meta-analysis, Trial Sequential Analysis, Stochastic Curtailment, Adaptive Design, Likelihood Ratio Test, and Bayesian Meta-analysis. Most studies focused on USRs (72.5%) and PMAs (98%). Trial Sequential Analysis was the most frequently encountered approach (46/51), while only one study described an extension to NMA. Methods varied widely in error control and ability to adjust for heterogeneity. While most approaches addressed type I error, fewer considered type II error or heterogeneity. This scoping review provides the first comprehensive mapping of methods for updated and living meta-analyses. Despite a range of available approaches, no single method demonstrated superiority across contexts. Further research should compare methods empirically, develop accessible software to support reliable, continuously updated evidence synthesis, and extend frameworks to NMA, especially as only a single methodological study was found for NMA.