TL;DR — Quick Answer
A literature review is a broad survey and synthesis of the existing research on a topic, providing context and identifying gaps. A systematic review is a more rigorous, structured type of review that follows a strict, predefined protocol to comprehensively identify, evaluate, and synthesise all relevant studies on a specific question, in order to minimise bias. The key difference is rigour and structure: a systematic review uses explicit, reproducible methods to answer a focused question, while a traditional literature review is broader and more flexible. Systematic reviews are considered a high level of evidence.
The terms “literature review” and “systematic review” are sometimes used as if they were interchangeable, but they refer to different things — and understanding the difference matters for both conducting and evaluating research. While both involve reviewing existing research, they differ significantly in their rigour, structure, purpose, and the confidence that can be placed in their conclusions. A systematic review is, in an important sense, a specific and especially rigorous kind of literature review.
Understanding what distinguishes a systematic review from a traditional literature review helps researchers choose the right approach for their needs and evaluate the reviews they encounter. This guide explains both types of review, how they differ, and when each is appropriate.
What Is a Literature Review?
A literature review is a survey and synthesis of the existing research on a topic. It identifies, summarises, and synthesises the relevant literature, providing an overview of what is known, identifying patterns and debates, and revealing gaps that new research can address. Literature reviews provide context for research, situating a study within the existing body of knowledge.
A traditional literature review is typically broad and flexible. It surveys the relevant literature on a topic, organised thematically, to provide a synthesised understanding of the current state of knowledge. The researcher selects and discusses the literature they judge relevant, with some flexibility in scope and approach. Traditional literature reviews are commonly found as part of theses, dissertations, and research papers, providing the background and justification for a study.
What Is a Systematic Review?
A systematic review is a specific, highly rigorous type of review that follows a strict, predefined protocol to comprehensively identify, evaluate, and synthesise all the relevant research on a focused question. Its defining feature is rigour and structure: it uses explicit, systematic, reproducible methods designed to minimise bias and provide a comprehensive, reliable synthesis of the evidence.
A systematic review begins with a clearly defined, focused question and a detailed protocol specifying exactly how the review will be conducted. It then systematically searches for all relevant studies using comprehensive search strategies, applies explicit criteria to select studies, critically appraises the quality of included studies, and synthesises the findings systematically. Every step is documented and reproducible.
This rigour makes systematic reviews a high level of evidence, particularly valued in fields like medicine and increasingly across other disciplines. Because they comprehensively and systematically synthesise the evidence while minimising bias, systematic reviews provide especially reliable conclusions about what the research collectively shows.
Systematic Review versus Literature Review
| Feature | Literature Review | Systematic Review |
|---|---|---|
| Approach | Broad, flexible | Strict, predefined protocol |
| Question | Broader topic | Focused, specific question |
| Search | Selective | Comprehensive, systematic |
| Study selection | Researcher’s judgement | Explicit predefined criteria |
| Bias | More susceptible | Designed to minimise |
| Reproducibility | Less reproducible | Reproducible |
| Evidence level | Lower | Higher |
The fundamental difference is rigour and structure. A systematic review follows a strict, transparent, reproducible protocol to comprehensively and objectively synthesise the evidence on a focused question, minimising bias. A traditional literature review is broader, more flexible, and more dependent on the researcher’s judgement, making it more susceptible to bias but also more adaptable. The systematic review trades flexibility for rigour and reliability.
Key Features of a Systematic Review
A Predefined Protocol
A systematic review is planned in advance through a detailed protocol specifying the question, search strategy, selection criteria, and methods. This predefined protocol, set before the review begins, is central to minimising bias, as decisions are made in advance rather than influenced by the results.
Comprehensive, Systematic Searching
A systematic review searches comprehensively for all relevant studies, using systematic search strategies across multiple databases and sources. The goal is to find all the relevant evidence, not just a selection, ensuring comprehensiveness.
Explicit Selection Criteria
A systematic review applies explicit, predefined criteria to decide which studies to include and exclude. These clear criteria, applied consistently, make the selection transparent and reproducible, reducing bias in which studies are considered.
Critical Appraisal
A systematic review critically appraises the quality of the included studies, assessing their methodological rigour. This evaluation of study quality informs how much weight the evidence carries and is part of the systematic, rigorous approach.
Systematic Synthesis
A systematic review synthesises the findings systematically, sometimes including a meta-analysis (a statistical combination of results across studies). This systematic synthesis provides a comprehensive, reliable picture of what the evidence collectively shows.
When to Use Each
A traditional literature review is appropriate when you need to survey and synthesise the literature on a topic broadly — to provide context for a study, understand the current state of knowledge, identify gaps, or situate research within the field. This is the kind of review found in most theses, dissertations, and research papers, providing background and justification. Its breadth and flexibility suit this purpose.
A systematic review is appropriate when you need a comprehensive, rigorous, unbiased synthesis of all the evidence on a focused question — particularly when the goal is to reach reliable conclusions about what the research collectively shows, to inform practice or policy, or to provide a high level of evidence. Systematic reviews are substantial undertakings requiring significant time and rigour, suited to questions where comprehensive, reliable synthesis is needed.
As Dr. Madhuri Kanojiya, Founder of Empire Research Press, explains: “The difference between a literature review and a systematic review is essentially the difference between a broad survey and a rigorous, reproducible investigation. A literature review synthesises the field flexibly to provide context; a systematic review follows a strict protocol to comprehensively and objectively answer a focused question while minimising bias. Both are valuable, but for different purposes. Know which you need: a literature review to situate your research, or a systematic review when you need the most reliable possible synthesis of the evidence.”
A Note on Other Review Types
Beyond these two, other review types exist, including scoping reviews (which map the breadth of literature on a broad topic), meta-analyses (which statistically combine results, often as part of systematic reviews), and narrative reviews (a term sometimes used for traditional literature reviews). The landscape of review types is varied, but the fundamental distinction between the flexible, broad literature review and the rigorous, structured systematic review captures the most important difference. Understanding where a review sits on this spectrum of rigour helps in both conducting and evaluating reviews.
Conclusion
A literature review is a broad, flexible survey and synthesis of the existing research on a topic, providing context and identifying gaps. A systematic review is a more rigorous, structured type of review that follows a strict, predefined protocol to comprehensively identify, evaluate, and synthesise all relevant studies on a focused question, minimising bias. The key difference is rigour and structure: the systematic review uses explicit, reproducible methods, while the traditional literature review is broader and more dependent on judgement.
Both types of review are valuable, but for different purposes — the literature review to situate and contextualise research, the systematic review to provide a comprehensive, reliable synthesis of the evidence. Understanding the difference helps researchers choose the right approach and evaluate the reviews they encounter. As a high level of evidence, the systematic review represents the most rigorous form of reviewing research, while the literature review remains an essential, flexible tool for understanding and situating a field.
Frequently Asked Questions
Q: What is the difference between a literature review and a systematic review?
A literature review is a broad, flexible survey and synthesis of the existing research on a topic, providing context and identifying gaps, with the researcher selecting relevant literature using their judgement. A systematic review is a more rigorous, structured type of review that follows a strict, predefined protocol to comprehensively identify, evaluate, and synthesise all relevant studies on a focused question, using explicit, reproducible methods designed to minimise bias. The key difference is rigour and structure: the systematic review is comprehensive, transparent, and reproducible, while the literature review is broader and more dependent on judgement. Systematic reviews are considered a higher level of evidence.
Q: What is a systematic review?
A systematic review is a highly rigorous type of review that follows a strict, predefined protocol to comprehensively identify, evaluate, and synthesise all the relevant research on a focused question. Its defining features are rigour and structure: it begins with a clearly defined question and detailed protocol, systematically searches for all relevant studies, applies explicit criteria to select them, critically appraises their quality, and synthesises the findings systematically — sometimes including a meta-analysis. Every step is documented and reproducible, designed to minimise bias. This rigour makes systematic reviews a high level of evidence, particularly valued in medicine and increasingly across other disciplines for providing reliable conclusions about what research collectively shows.
Q: When should I do a systematic review instead of a literature review?
You should do a systematic review when you need a comprehensive, rigorous, unbiased synthesis of all the evidence on a focused question — particularly when the goal is to reach reliable conclusions about what research collectively shows, to inform practice or policy, or to provide a high level of evidence. A traditional literature review is more appropriate when you need to survey the literature broadly to provide context for a study, understand the current state of knowledge, identify gaps, or situate research within the field, as in most theses and research papers. Systematic reviews are substantial undertakings requiring significant time and rigour, suited to questions where comprehensive, reliable synthesis is genuinely needed.
Q: Why are systematic reviews considered high-quality evidence?
Systematic reviews are considered high-quality evidence because they comprehensively and systematically synthesise all the relevant research on a focused question while minimising bias. They follow a strict, predefined protocol, search comprehensively for all relevant studies, apply explicit selection criteria, critically appraise study quality, and synthesise findings systematically — with every step documented and reproducible. This rigour means their conclusions are based on the totality of the evidence rather than a selective or biased sample, and the reproducible methods allow others to verify them. By comprehensively and objectively combining the evidence, systematic reviews provide especially reliable conclusions, which is why they sit high in evidence hierarchies, particularly in medicine.
Q: What is a meta-analysis?
A meta-analysis is a statistical technique that combines the results of multiple studies to produce an overall quantitative estimate of an effect. It is often conducted as part of a systematic review, statistically pooling the findings of the included studies to reach a combined conclusion that is more precise and powerful than any single study. By combining data across studies, a meta-analysis can provide a stronger, more reliable estimate of an effect than individual studies alone. Meta-analysis is distinct from but often associated with systematic reviews — the systematic review comprehensively identifies and evaluates the studies, while the meta-analysis statistically combines their results, together providing a high level of evidence.
Article reviewed, edited, fact-checked and approved before publication. — Empire Research Press Editorial Standard