Types of Research Reviews: Literature Reviews, Systematic Reviews, and Scoping Reviews Explained

Literature Review – No strict system; risk of bias – It is informal, narrative, and selective – Purpose: to show what’s known, critique, and frame your research

Systematic Review – Question must be very clear and focused – Use pre-specified criteria, structured methods, and critical appraisal – Aim: find all evidence matching criteria + synthesize objectively

Scoping Review – Question is broad/exploratory, less precise – Want to see what has been done in the field: map concepts, coverage, gaps – Less emphasis on critical appraisal; more on overview and mapping

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Literature Review A literature review is a structured summary, synthesis, and critical evaluation of previously published works on a particular topic. It aims to map what is known, identify gaps, clarify debates, and situate the current research in the context of existing scholarship. (Purdue OWL)

Key features:

• It does not usually attempt to locate all evidence exhaustively, but focuses on the most relevant and influential sources.

• It is often narrative and interpretive, organizing literature thematically, chronologically, or methodologically.

• It serves to contextualize and justify a research question or project, showing where your work fits and what contributes new insight.
  

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Systematic Review“A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question.” (Cochrane Library)

Expanded definition:

A systematic review is a methodical and reproducible approach to reviewing literature. It:

• Uses explicit, pre-specified inclusion and exclusion criteria.

• Conducts a comprehensive search of multiple sources (databases, grey literature) to find all relevant studies.

• Critically appraises the methodological quality (risk of bias) of included studies.

• Synthesizes findings (often quantitatively via meta-analysis, or qualitatively via narrative synthesis) to present a coherent answer or conclusion.

• Seeks to minimize bias and maximize transparency and reproducibility. (Wikipedia)
  

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Scoping Review A scoping review systematically searches, selects, and charts available evidence, without necessarily critically appraising all included studies, to map concepts, types of evidence, and gaps in a given field. (training.cochrane.org)

Characteristics:

• Broader in scope than a systematic review; less focused on a narrow question. (Simply Psychology)

• May include various types of evidence (quantitative, qualitative, theoretical) without restricting to certain designs. (training.cochrane.org)

• Critical appraisal (risk of bias) is often optional or lighter than in systematic reviews. (BioMed Central)

• Useful as a preliminary step to a systematic review—helping to identify how best to define questions, inclusion criteria, and gaps in the literature. (BioMed Central)

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Literature Review

• Less formal, more flexible

• What to include: major theories, key studies, debates, gaps, methodologies used, and conceptual frameworks

• Purpose: provide context, background, and rationale for your own research
  

Systematic Review

• The research question must be very precise

• Use PICO (or variants like PICOS, PICOT) or DDO frameworks to define eligibility and guide analysis

  PICO = Population / Intervention / Comparison / Outcome (Cochrane Library)DDO = Domain / Determinant / Outcome — useful especially in observational, etiologic, diagnostic, prognostic studies (i.e., where “intervention vs control” is not exactly appropriate) (Uniqcret)

• Steps include:  • Define inclusion/exclusion criteria using PICO (or DDO)  • Comprehensive search across databases + grey literature  • Critical appraisal (assess risk of bias)  • Data extraction & synthesis (often meta-analysis or structured narrative)
  

Scoping Review

• The research question is broad/exploratory — you want to see what has been done in a field

• Use PCC to shape the question and eligibility

  PCC = Population / Concept / Context (ScienceDirect)

  • Population = which people or groups

  • Concept = what phenomenon, idea, intervention, exposure, topic

  • Context = setting, environment, circumstances, geographic or institutional scope

• Steps include:  • Identify and chart (map) existing literature  • No (or limited) critical appraisal  • Summarize types of evidence, gaps, research designs, and trends • Use findings to inform future research (e.g., to refine a systematic review question)

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A systematic review is different from a scoping review

(Munn et al., 2018)

Feature	Traditional review	Scoping review	Systematic review
A priori review protocol	No	Yes (some)	Yes
PROSPERO registration	No	No	Yes
Explicit, transparent search strategy	No	Yes	Yes
Standardized data extraction forms	No	Yes	Yes
Mandatory critical appraisal	No	No	Yes
Synthesis of findings from individual studies and summary of findings	No	No	Yes