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 analysisPICO = 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 eligibilityPCC = 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)