Skip to Main Content

Systematic Reviews & Evidence Synthesis

Evidence Synthesis Reviews

Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies. Systematic Review is the most commonly referred-to type of evidence synthesis and is sometimes confused as a blanket term for other types of reviews. For help in selecting a methodology, try the review methodology decision tree from Cornell University.

Types of evidence synthesis include:

Systematic Review

  • Exhaustive review of primary evidence on a clearly formulated question of medical, scientific, policy or management importance 
  • Methods must be transparent, reproducible and follow an established protocol
  • Requires a team and time commitment. Time-intensive often taking months to a year or more to complete

Literature (Narrative) Review

  • A broad term referring to reviews with a wide scope and non-standardized methodology 
  • Search strategies, comprehensiveness, and time range covered will vary and do not follow an established protocol
  • Can be conducted by an individual or a team

​Scoping Review or Evidence Map

  • Systematically and transparently collect and categorize existing evidence on a broad question of policy or management importance
  • Seeks to identify research gaps and opportunities for evidence synthesis rather than searching for the effect of an intervention 
  • May critically evaluate existing evidence, but does not attempt to synthesize the results in the way a systematic review would (see EE Journal and CIFOR)
  • Requires a team and time commitment; may take longer than a systematic review
  • See Arksey and O'Malley (2005) for methodological guidance

Rapid Review

  • Applies Systematic Review methodology within a time-constrained setting (often ≤ 3 months)
  • Employs methodological "shortcuts" (e.g., limiting search terms) at the risk of introducing bias
  • Useful for addressing issues needing quick decisions, such as developing policy or treatment recommendations for emergent conditions
  • See Evidence Summaries: The Evolution of a Rapid Review Approach

Umbrella Review

  • Reviews other systematic reviews on a topic 
  • Often defines a broader question than is typical of a traditional systematic review
  • Most useful when there are competing interventions to consider

Meta-analysis

  • Statistical technique for combining the findings from disparate quantitative studies
  • Uses statistical methods to objectively evaluate, synthesize, and summarize results
  • May be conducted independently or as part of a systematic review

Adapted from Cornell University Library's A Guide to Evidence Synthesis: Types of Evidence Synthesis

Select a type of evidence synthesis project based on the goals of your project, available resources to meet methodological guidelines, existing data quality and quantity, and other similar objective reasons.

Tools for Review Type Selection

Decision tree for selecting the appropriate type of literature review

Image developed by Anna Ferri (anna.ferri@colostate.edu) at Colorado State University and licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Methodology

  • Barry, E.S., Merkebu, J., and Varpio, L. (2022). State-of-the-art literature review methodology: A six-step approach for knowledge synthesis. Perspectives on Medical Education, 11(5), 281-288. https://doi.org/10.1007/s40037-022-00725-9 (open access)
  • Fromm, Y.M., Martin, F., Gezer, T. et al. (2025). Best Practices for Conducting Systematic Reviews: Perspectives of Experienced Systematic Review Researchers in Educational Sciences. Technology, Knowledge and Learning 30, 1–28. https://doi.org/10.1007/s10758-025-09819-9 (open access)
  • Ibrahim, A., Khan, T., LaJeunesse, D., Obare, S. and Dellinger, A. (2025). Nanoscience systematic review methodology standardization. Nanotechnology Reviews, 14(1), 20250144. https://doi.org/10.1515/ntrev-2025-0144 (open access)
  • Mohamed Shaffril, H. A., Samsuddin, S. F., and Abu Samah, A. (2021). The ABC of systematic literature review: the basic methodological guidance for beginners. Quality & Quantity, 55(4), 1319–1346. https://doi.org/10.1007/s11135-020-01059-6

About reviews types

  • Grant, M.J. and Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies.  Health Information and Libraries Journal, 26(2) 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x (open access)
  • Gough, D., Thomas, J. and Oliver, S. (2012). Clarifying differences between review designs and methods. Systematic Reviews, 1, article number 28. https://doi.org/10.1186/2046-4053-1-28 
  • Moher, D., Stewart, L., and Shekelle, P. (2015). All in the Family: systematic reviews, rapid reviews, scoping reviews, realist reviews, and more. Systematic Reviews, 4, article number 183. https://doi.org/10.1186/s13643-015-0163-7 (open access)
  • Sutton, A., Clowes, M., Preston, L. and Booth, A. (2019). Meeting the review family: exploring review types and associated information retrieval requirements. Health Information and Libraries Journal, 36(3) 202-222. https://doi.org/10.1111/hir.12276 (open access)

Systematic reviews

  • Cho, Y. (2022). Comparing Integrative and Systematic Literature Reviews. Human Resource Development Review, 21(2), 147-151. https://doi.org/10.1177/15344843221089053 (open access)
  • Lodge, M. (2011). Conducting a systematic review: Finding the evidence. Journal of Evidence-Based Medicine, 4(2), 135–139. https://doi.org/10.1111/j.1756-5391.2011.01130.x (open access)
  • Munn, Z., Peters, M.D.J., Stern, C. et al. (2018). Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Medical Research Methodology, 18, article number 143. https://doi.org/10.1186/s12874-018-0611-x (open access)
  • Munn, Z., Stern, C., Aromataris, E., Lockwood, C., & Jordan, Z. (2018). What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences. BMC Medical Research Methodology, 18, article number 5. https://doi.org/10.1186/s12874-017-0468-4 (open access)

Literature (Narrative) reviews

  • Baethge, C., Goldbeck-Wood, S. and Mertens, S. (2019). SANRA—a scale for the quality assessment of narrative review articles. Research Integrity and Peer Review, 4, article number 5. https://doi.org/10.1186/s41073-019-0064-8 (open access)
  • Greenhalgh, T., Thorne, S., & Malterud, K. (2018). Time to challenge the spurious hierarchy of systematic over narrative reviews? European Journal of Clinical Investigation, 48(6), e12931-n/a. https://doi.org/10.1111/eci.12931 (open access)
  • Haddaway, N. R., Woodcock, P., Macura, B., and Collins, A. (2015). Making literature reviews more reliable through application of lessons from systematic reviews. Conservation Biology, 29(6), 1596–1605. https://doi.org/10.1111/cobi.12541 

Scoping reviews

  • Arksey, H. and O'Malley, L. (2005). Scoping Studies: Towards a Methodological Framework. International Journal of Social Research Methodology, 8(1), 19-32. https://doi.org/10.1080/1364557032000119616 
  • Campbell, F., Tricco, A.C., Munn, Z. et al. (2023). Mapping reviews, scoping reviews, and evidence and gap maps (EGMs): the same but different— the “Big Picture” review family. Systematic Reviews, 12, article number 45. https://doi.org/10.1186/s13643-023-02178-5  (open access)
  • Khalil, H., Peters, M. D., Tricco, A. C., Pollock, D., Alexander, L., McInerney, P., Godfrey, C. M., and Munn, Z. (2021). Conducting high quality scoping reviews-challenges and solutions. Journal of Clinical Epidemiology, 130, 156–160. https://doi.org/10.1016/j.jclinepi.2020.10.009 [Open access version]
  • Khalil, H. and Tricco, A.C. (2022). Differentiating between mapping reviews and scoping reviews in the evidence synthesis ecosystem. Journal of Clinical Epidemiology, 149, 175-182. https://doi.org/10.1016/j.jclinepi.2022.05.012 
  • Munn, Z., Pollock, D., Khalil, H., Alexander, L., Mclnerney, P., Godfrey, C. M., Peters, M., and Tricco, A. C. (2022). What are scoping reviews? Providing a formal definition of scoping reviews as a type of evidence synthesis. JBI Evidence Synthesis, 20(4), 950–952. https://doi.org/10.11124/JBIES-21-00483 (open access)

Rapid Review

  • Hamel, C., Michaud, A., Thuku, M., Skidmore, B., Stevens, A., Nussbaumer-Streit, B., and Garritty, C. (2021). Defining Rapid Reviews: a systematic scoping review and thematic analysis of definitions and defining characteristics of rapid reviews. Journal of Clinical Epidemiology, 129, 74–85. https://doi.org/10.1016/j.jclinepi.2020.09.041 
  • Khangura, S., Konnyu, K., Cushman, R., Grimshaw, J., and Moher, D. (2012). Evidence summaries: the evolution of a rapid review approach. Systematic Reviews, 1, article number 10. https://doi.org/10.1186/2046-4053-1-10 (open access) 

Umbrella Review

  • Belbasis, L., Bellou, V., and Ioannidis, J. P. A. (2022). Conducting umbrella reviews. BMJ Medicine, 1, e000071. https://doi.org/10.1136/bmjmed-2021-000071 (open access) 
  • Smith, V., Devane, D., Begley, C. M., and Clarke, M. (2011). Methodology in conducting a systematic review of systematic reviews of healthcare interventions. BMC Medical Research Methodology, 11, article number 15. https://doi.org/10.1186/1471-2288-11-15 (open access)