Scoping Review or Systematic Review: The Question Decides
A scoping review is not a systematic review with lower standards. What each design can answer, and the three signs you have chosen the wrong one.
Scoping reviews are sometimes chosen because they seem easier: no meta-analysis, no risk-of-bias assessment, less statistical work. That is the wrong reason, and it produces reviews that satisfy nobody.
The two designs answer different questions, and the question should decide.
What each one answers
A systematic review answers a focused question about effect, accuracy or association, usually structured as PICO, and synthesises the findings of eligible studies. It appraises study quality because the answer depends on how reliable the studies are.
A scoping review maps what evidence exists on a topic, how it has been produced, and where the gaps are. Munn and colleagues (2018) set out the indications: examining the extent and nature of a body of research, clarifying concepts or definitions, identifying key characteristics of a field, and identifying gaps as a precursor to a systematic review.
The unit of interest differs. A systematic review is interested in what the studies found. A scoping review is interested in what the studies are.
Three signs of a wrong choice
You are running a scoping review but your discussion draws conclusions about whether the intervention works. That is a systematic review question, and answering it without appraisal or synthesis is the failure mode scoping reviews are criticised for.
You are running a systematic review but your inclusion criteria admit five incompatible study designs measuring eight different outcomes. There is nothing to pool, and the result will be a narrative summary with a systematic review's overheads. A scoping review was the right design.
You planned a systematic review and the search returned 4,000 records across a heterogeneous literature with no comparable outcomes. This one is discovered mid-project, and switching to a scoping review is a legitimate response provided it is declared as a protocol deviation with reasons.
What scoping reviews still require
The absence of meta-analysis does not mean the absence of method.
- A protocol, registered where the registry accepts scoping reviews. PROSPERO does not; the Open Science Framework and Figshare do, and several journals publish protocols.
- A search as systematic as any other, reported to PRISMA-S standard.
- Duplicate screening, or a stated and justified alternative.
- A charting form, piloted before use, and a stated approach to synthesising the charted data.
- Reporting to PRISMA-ScR, which is the extension covering this design.
The JBI methodology, which most scoping reviews follow, builds on the Arksey and O'Malley framework and the refinements Levac and colleagues proposed. Critical appraisal is optional in a scoping review rather than absent by definition, and where it is omitted the reason should be stated rather than left implicit.
The consultation stage
Arksey and O'Malley's framework includes an optional consultation exercise with stakeholders, and Levac and colleagues argued it should be a required component rather than an optional extra.
It is skipped in most published scoping reviews. Where the review is intended to inform a research agenda or a service decision, including it materially improves the relevance of the mapping, and it distinguishes a scoping review that will be used from one that will be cited.
A note on other designs
Two adjacent options are worth knowing about.
An evidence and gap map presents the same information as a scoping review in a visual matrix of interventions against outcomes, and is more useful than prose when the purpose is to show where evidence is missing.
A rapid review applies systematic methods with explicit, declared shortcuts to meet a decision deadline. It is a legitimate design when the shortcuts are stated and their likely effect discussed, and it is not a euphemism for a review done carelessly.
References
Arksey, H., & 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
Levac, D., Colquhoun, H., & O'Brien, K. K. (2010). Scoping studies: Advancing the methodology. Implementation Science, 5, 69. https://doi.org/10.1186/1748-5908-5-69
Munn, Z., Peters, M. D. J., Stern, C., Tufanaru, C., McArthur, A., & Aromataris, E. (2018). Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Medical Research Methodology, 18, 143. https://doi.org/10.1186/s12874-018-0611-x
Tricco, A. C., Lillie, E., Zarin, W., O'Brien, K. K., Colquhoun, H., Levac, D., Moher, D., Peters, M. D. J., Horsley, T., Weeks, L., Hempel, S., Akl, E. A., Chang, C., McGowan, J., Stewart, L., Hartling, L., Aldcroft, A., Wilson, M. G., Garritty, C., … Straus, S. E. (2018). PRISMA extension for scoping reviews (PRISMA-ScR): Checklist and explanation. Annals of Internal Medicine, 169(7), 467–473. https://doi.org/10.7326/M18-0850
Common questions
- Can a scoping review include a meta-analysis?
- Generally no, and if pooling is what you want, the question is a systematic review question. Some scoping reviews report descriptive quantitative summaries of study characteristics, such as how many studies used a given outcome measure, which is charting rather than synthesis.
- Do I need to appraise quality in a scoping review?
- It is optional under JBI guidance and PRISMA-ScR. Where the review will inform practice rather than only mapping the literature, appraisal adds value. State the decision and its rationale either way.
- Can a scoping review be published in a good journal?
- Yes, and well-conducted ones are widely cited because they save other teams months of orientation. Several of the collections currently open for submissions explicitly welcome scoping reviews and evidence maps.