Developing a standardized, expert-validated taxonomy and evidence hierarchy for review typologies: a multi-methods study

Abstract

Numerous review typologies currently exist in the scientific literature. Inconsistent terminology, overlapping objectives, and variable methodological structures may complicate the selection process for researchers. Existing evidence hierarchies primarily address primary studies and often do not account for the methodological characteristics of review typologies. Aims To develop a standardized, expert-validated taxonomy for review typologies and construct an evidence hierarchy ranking them by inherent methodological rigor and evidence certainty. Methods A multi-methods design was used. A systematic review of six databases (PubMed/MEDLINE, Scopus, Web of Science, EMBASE, ProQuest, Cochrane Library) and grey literature identified 70 distinct review typologies. These were refined via a three-round Delphi process by 67 international experts from 30 countries. The process achieved strong consensus (Kendall's W = 0.90). Each typology was appraised using adapted GRADE and ROBIS tools applied to methodological procedures, not individual reviews. A pre-specified composite scoring algorithm (Faulkner et al., 2022; Lee, 2019; Haidich, 2010; Grant and Booth, 2009; Lachal et al., 2017; Botes, 2002; Hellman, 2024; Bartolucci and Hillegass, 2010; Moons et al., 2021 [2–10]) integrating GRADE certainty and ROBIS risk-of-bias judgments determined placement within a three-tier hierarchy. Results The systematic literature review yielded 3462 records, identifying 70 distinct review typologies. Following expert consolidation, 13 functionally distinct typologies emerged, classified into a three-tier evidence hierarchy. Tier 1 (high-certainty) included meta-analyses and review overviews; Tier 2 (moderate-certainty) included systematic, scoping, rapid, and RE-AIM reviews; Tier 3 (low-certainty) included narrative, realist, integrative, and mapping reviews. This hierarchical ranking reflects a methodological rigor gradient, with scores rising from exploratory, flexible typologies to rigorous, protocol-driven methods. Conclusion This study proposes a taxonomy of review typologies organized within a three-tier hierarchy. By linking expert-derived typology definitions with standardized methodological rigor assessments, the framework enhances clarity, comparability, and transparency across evidence synthesis. It provides a practical foundation for selecting appropriate typologies and supports consistent, reliable evidence-based decision-making across research, clinical practice, and policy. Future research should prioritize empirically validating this framework across diverse disciplinary contexts and developing automated tools supporting its implementation. Implication for clinical practice This validated three-tier taxonomy equips clinicians to rapidly appraise synthesis rigor, anchoring evidence-based practice to the most methodologically robust literature.