The need for practical literature synthesis in evidence-based disciplines is skyrocketing in today's research landscape. As researchers, students, and institutions wander through an ever-widening expanse of knowledge, it is equally important to familiarize themselves with the tools that can help them analyze and summarize the literature.
Two key methods, scoping reviews, and systematic reviews, often generate confusion due to their similarities. However, these approaches serve different purposes and offer unique benefits.
This article gives a fairly clear understanding of the definitions, key differences, applications, and practical guidance in choosing the right review type. Whatever field you're working on, whether it is healthcare or social sciences, understanding when and how to apply these can make an enormous difference to your research.
What is a scoping review?
Definition and goals
A scoping review is a literature review on broad topics already in the literature. Instead of attempting to answer a specific research question, it seeks to provide an overview of the nature and scope of existing evidence in a certain area. Such reviews are often meant to describe fundamental concepts and theories, highlight knowledge gaps, and propose areas for future research.
A scoping review is meant to give the field a breadth of understanding rather than to assess studies critically; this is more valuable when studies within the particular research area are rather fragmented or underdeveloped, acting as background work for future, more specific studies.
Structure and approach
Scoping reviews are conducted with a broad and flexible methodology designed to map out the scope of existing literature in a particular field. Scoping reviews differ because they take a more exploratory route than systematic reviews, which are more direct in answering a specific question. Here's how scoping reviews are typically carried out:
- Broad search strategy: The search strategy utilized in a scoping review is quite wide-ranging and includes many types of literature, such as peer-reviewed journal articles, grey literature (like reports, theses, and conference papers), and sometimes unpublished studies. The advantage of this flexibility is that a fuller inventory is attempted even when some studies are not easy to access or do not fall within standard publishing routes.
- Inclusion/exclusion criteria: While the inclusion and exclusion criteria are still defined, they tend to be less rigid than in systematic reviews. Achieving the goals entails casting a wide net and catching in as many pertinent studies as possible to grasp a topic's broader landscape. At this point, researchers often prefer breadth over depth.
- Data extraction: Scoping reviews do not focus on detailed data extraction like systematic reviews. Instead, relevant information concerning the study's aims, methods, and key findings is gathered to identify overarching trends, themes, and knowledge gaps in the field.
- Narrative synthesis: The results of a scoping review are typically presented in a narrative synthesis rather than statistical analysis. The synthesis focuses on summarizing the range of research findings and providing insights into the broader context.
This flexibility is also relevant as it allows researchers to adapt their approach to the available literature and the research question(s) they wish to study.
Use cases
Scoping reviews are particularly useful in the following:
- Emerging or poorly defined fields: When the research area is new, a scoping review can help define the research parameters and set ground knowledge.
Example: In the field of artificial intelligence in healthcare, a scoping review could identify current applications, challenges, and areas that require further exploration, such as AI's ethical implications.
- Clarifying concepts: They are also helpful in defining terms, populations, or interventions without consensus.
Example: A scoping review in public health might help clarify the definitions of "mental health" across studies, providing clarity for future research to use consistent terminology.
- Identifying gaps: Scope reviews can point out areas where too little research has been done, thus fostering opportunities for forthcoming systematic reviews.
Example: A scoping review of environmental policy might reveal a lack of research on climate change's impacts on urban populations, signaling a need for future, more focused studies on this issue.
What is a systematic review?
Definition and intent
A more focused and structured systematic review is designed to answer specific questions. Unlike scoping reviews, systematic reviews aim to gather, appraise, and synthesize evidence based on a particular methodology. This review type answers precise questions, often related to the effectiveness of an intervention, the diagnostic accuracy of a test, or the relationship between variables.
Methodological rigor
Systematic reviews follow a highly structured process, which includes:
- Protocol registration: The review protocol is registered ahead of time to minimize bias and ensure all aspects of the review are transparent.
- Structured search strategies: Systematic reviews use a comprehensive and reproducible search strategy to identify all relevant studies.
- Quality assessments: Every included study is assessed for methodological quality or risk of bias using established criteria.
Common applications
Systematic reviews are critical in fields such as:
- Healthcare: For evaluating clinical interventions, treatment efficacy, and diagnostic accuracy.
- Public Health: To assess public health policies or interventions to improve community well-being.
- Education: To synthesize evidence on teaching methods or educational programs.
Core differences between scoping and systematic reviews
Purpose and scope
While both types of reviews involve literature synthesis, the key difference lies in their purpose and scope.
Scoping reviews were used to explore the breadth of literature on a broad topic. They map out the existing research landscape in terms of gaps in knowledge and the different concepts, terminologies, and study designs used. Research questions in scoping reviews are generally open-ended and broad since they aim to capture the breadth of a field or provide an overview of a subject area.
Systematic reviews, in contrast, have a rigorous approach to answering the focused and particular questions they attempt to cover. Such reviews aim to gather all available evidence on a narrowly defined topic, usually directed at appraising the effectiveness of interventions, establishing causal links, or judging the quality of the evidence.
Questions in systematic reviews of necessity become far more structured and, therefore, require somewhat of a targeted approach in data gathering.
Search strategy and inclusion criteria
The way each review type approaches searching the literature and applying inclusion/exclusion criteria varies significantly.
Scoping reviews typically have a broad search strategy. Researchers aim to include a wide range of studies, sometimes without limiting by study type or quality. Generally, the criteria consider malleability to allow for flexibility in obtaining as much relevant information as possible, ultimately allowing a broad overview of the topic.
By contrast, systematic reviews follow a much more detailed and rigid search strategy. Researchers set strict inclusion and exclusion criteria based on the research question.
Therefore, the systematic review strategy ensures that lesser quality studies are excluded from those specifically predefined criteria. This often involves multiple database searches and strict filters based on study design, language, and publication type.
Data handling and analysis
The way each review type handles and analyzes the data gathered from the literature is another key difference.
Scoping reviews' main purpose is to summarize the characteristics and findings of the selected studies without necessarily providing a detailed analysis. The extracted data are generally descriptive in nature and aim to map trends, identify research gaps, and provide large-scale contextualization.
Systematic reviews involve a more structured and detailed data analysis. This includes evaluating the methodological quality of studies, conducting statistical analysis (such as meta-analysis), and synthesizing the results to directly answer the research question. The analysis is rigorous, with systematic data extraction and quality assessment protocols.
Assessment of evidence quality
A critical difference between scoping and systematic reviews is their approach to assessing the quality of evidence.
Scoping reviews do not generally assess the quality of the included studies. Since the purpose is to map the literature broadly and identify trends or gaps, scoping reviews do not focus on the methodological rigor or potential biases in individual studies.
Systematic reviews, however, critically appraise each study's quality. Researchers assess the risk of bias, methodological rigor, and relevance of studies included in the review. The quality of the evidence is typically rated using established frameworks, such as the GRADE system, and included in the final synthesis of results.
Outcomes and reporting
Scoping reviews provide a broad narrative summary of the literature. The outcome is usually a map or framework that categorizes existing studies, identifies research gaps, and outlines key themes or concepts. The findings are often presented descriptively without detailed statistical synthesis.
In contrast, systematic reviews focus on delivering a comprehensive and conclusive synthesis of the evidence. The findings are typically organized into clear sections, with detailed evidence summaries, statistical results (if applicable), and discussions on the implications for practice or policy. Systematic reviews provide more definitive conclusions and are often used to guide decision-making.
Time and resource implications
Scoping reviews tend to be less time-consuming and resource-intensive. Due to their broad nature, researchers may not need rigorous data extraction or statistical analysis. The process may take less time, as the inclusion criteria are more flexible, and the focus is on mapping existing studies rather than synthesizing detailed evidence.
Systematic reviews are more resource-demanding and time-consuming. They require a meticulous process of literature searching, study selection, data extraction, quality appraisal, and synthesis. The work involved in ensuring that only the highest-quality studies are included, coupled with the need for statistical analysis, makes systematic reviews significantly more time—and resource-intensive.
When to choose a scoping review
Early-stage research exploration
Scoping reviews are ideal when the emerging research field lacks sufficient studies to form conclusive evidence. They help map the scope of existing research and identify areas for future inquiry.
Clarifying concepts or terminology
In fields where terminology or concepts are not well-defined, scoping reviews can help clarify terms and understand how they are applied across various studies.
Mapping and identifying gaps
Scoping reviews are particularly useful when the goal is to identify research gaps. They provide a comprehensive literature overview, highlighting areas that need further exploration.
When to choose a systematic review
Answering specific research questions
Systematic reviews are the preferred method when the goal is to answer a narrow, well-defined research question. These reviews are designed to evaluate the effectiveness of an intervention, the accuracy of a diagnostic tool, or other precise inquiries.
Supporting evidence-based decision-making
Systematic reviews are essential in policymakers, healthcare providers, and other practitioners' decision-making processes. They provide reliable evidence to guide actions and policies.
When high methodological rigor is essential
Systematic reviews are required in academic publishing and regulatory contexts where high standards of evidence are necessary. Their structured approach ensures reliability and validity.
Can a scoping review lead to a systematic review?
Sequential review design
A scoping review can often serve as a precursor to a systematic review. After mapping out the existing literature and identifying gaps, a researcher may conduct a systematic review to address specific questions raised during the scoping process.
Strategic planning
Early scoping reviews inform the refinement of research questions and assess the feasibility of the systematic review, helping researchers more effectively plan the next steps.
Methodological considerations
Transitioning from a scoping to a systematic review requires careful methodological planning. Researchers must ensure that the broader findings from the scoping review align with the focused research questions of the systematic review.
Common misconceptions researchers should avoid
Scoping reviews are not ‘easier’
Many believe that scoping reviews are less rigorous and require less expertise. However, they still require careful planning, broad literature searches, and critical analysis of existing research.
Systematic reviews are not always necessary
Systematic reviews are not always required. Sometimes, simpler methods, such as a scoping review, may be sufficient to answer broad research questions or clarify concepts.
Choosing based on trend rather than fit
It is crucial to choose the review type based on the research goals, not simply the current trend. Understanding the purpose of each review type ensures that the correct method is applied to the research question.
How review selection impacts funding, publication, and impact
Funding considerations
Funding bodies may assess the relevance of a review type based on its goals and the type of evidence it generates. Systematic reviews often attract more funding due to their rigorous nature and ability to provide conclusive evidence.
Journal preferences and peer review
Journal requirements may vary depending on the review type. Due to their methodological rigor, systematic reviews are often favored in high-impact journals, while scoping reviews may be more appropriate for emerging fields.
Long-term impact and visibility
Systematic reviews tend to have a higher long-term impact, providing conclusive evidence that can influence policy, practice, and future research. Though valuable for mapping literature, scoping reviews may not have the same visibility or citation rates.
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