Literature review articles use database searches to identify, collate, and analyze available evidence on a topic. Systematic reviews, scoping reviews, and narrative reviews are different evidence-collection and synthesis approaches.
But which type of review is (and isn’t) right for your research question? And how reliable are the findings of different review types?
There are distinctive features, aims, and scope between systematic reviews, scoping reviews, and narrative reviews. Let’s look at each and then pair them up to know which one you’ll need, whether you need ideas and references or you’re looking to write your own review.
What you’ll learn in this post
• The difference (and similarity) between a systematic review, scoping review, and narrative review.
• The features and value of each of these types of review.
• Side-by-side feature comparison charts of each review type.
• Where to educate yourself on reviews, and how to get expert guidance from published researchers.
What is a systematic review?
Definition and history
We don’t have a universal or standard definition of systematic reviews. A systematic review usually is a critical assessment of all the literature addressing a well-defined question. It aims to give the best possible answer based on available evidence.
Systematic reviews follow structured and predefined methods to identify, appraise, and synthesize the relevant literature. They use specific inclusion and exclusion criteria based on strict protocols, such as the PRISMA statement or Cochrane Protocol.
A meta-analysis is a systematic review that, in addition to a narrative summary, combines all the studies’ results into a single statistical analysis. The PRISMA 2020 Checklist offers guidance on how to conduct a meta-analysis.
Systematic reviews ensure that the results are reliable and meaningful to end-users, so they’re widely considered the strongest source for evidence-based healthcare.
Systematic reviews have been widely used since then. They are necessary for clinicians to keep up to date with their field. They are also often used to inform the development of clinical guidelines and practice.
Key functions and features
A systematic review aims to:
- Uncover the international evidence on a particular topic
- Confirm current practice; address uncertainty or variation in practice; identify new practices
- Find and inform areas for future research
- Locate and investigate mixed or conflicting results
- Produce statements to guide decision-making
Traditionally, researchers mainly carried out systematic reviews to assess the effectiveness of health interventions. In this respect, PROSPERO serves as an international database of registered systematic reviews in health and social care sciences. Or in other fields where there is a health-related outcome.
A 2020 systematic review appraising the most effective interventions for depression in heart failure patients is a good example of this approach. They explored six common interventions, medical and non-medical. It found that collaborative care and psychotherapy were the most effective treatments.
But systematic reviews have gone beyond assessing a treatment’s feasibility, appropriateness, meaningfulness, or effectiveness. They’re widely used to measure the cost-effectiveness or impact of socioeconomic interventions.
This review gives an economic appraisal of the clinical outcomes and economic effectiveness of different economic evaluations used for pharmacy services studies in health systems. It found these evaluations are increasingly used to understand which healthcare services provide value for money amid limited healthcare resources.
What is a scoping review?
Definition and history
Systematic reviews are essential for robustly addressing specific questions. But sometimes they might not be able to meet your specific aims or research project requirements. Or you might need a methodologically rigorous and structured preliminary scoping activity to inform how future systematic reviews are done.
That’s where scoping reviews come into play. They’re sometimes called scoping exercises/scoping studies. Scoping reviews rapidly map the size, characteristics, or scope of existing literature in a field of interest. They can help you locate research gaps and needs.
Scoping reviews are “younger” than systematic reviews. They emerged in the early 2000s. There used to be some confusion around their definition and the steps involved in the scoping review process. But, in 2015, a methodological working group of the JBI produced formal guidance for conducting scoping reviews. Likewise, the PRISMA extension for scoping reviews was published in 2018.
Key functions and features
Researchers usually carry out a scoping review to:
- Identify the types of evidence in a given field. For example, a scoping review by Challen et al. sought to find the types of available evidence regarding the source and quality of publications and grey literature around emergency planning.
- Clarify crucial concepts or terms in the literature.
- Examine how research is conducted on a specific topic or field. A scoping review of that kind explored the scope of the literature around interventions aimed to improve health care quality in populations with osteoarthritis.
- Identify key characteristics or factors related to a concept.
- As a precursor to a systematic review (examining emerging evidence to confirm the relevance of inclusion criteria and potential questions).
- Identify and analyze knowledge gaps.
What is a narrative review?
A narrative review is a thorough and critical overview of previously published research on the author’s specific topic of interest. It’s also referred to as a traditional review or a literature review.
Narrative reviews are helpful in the following ways:
- You can read them as a general and accurate guide to what is already known about a given topic.
- They are a key part of the research process. They help you establish a theoretical and methodological framework or context for your research.
- By doing a literature review, you can locate existing patterns and trends. This helps you find the gaps in your field and formulate a meaningful research question.
So, like the systematic and scoping reviews, a narrative review appraises, critiques, and summarizes a topic’s available research.
For example, this narrative review sums up the evidence on exercise interventions in improving the health aspects of patients with preclinical Alzheimer’s disease. This narrative review is provided for the clinical development programs for non-oral, non-injectable formulations of dihydroergotamine (DHE) to treat migraine.
But, narrative reviews are far less systematic and rigorous. They’re evidence-based but not always considered massively helpful in terms of the scientific evidence they bring. They’re much more prone to selection bias.
For example, a review paper comparing seven narrative reviews with two systematic reviews found that narrative reviews of the same studies reached different conclusions. So, when you read or assess a narrative review, watch out for certain biases in data search methods.
Main differences between a systematic review and a scoping review
Systematic reviews and scoping reviews similarly use rigorous and transparent methods to comprehensively identify and analyze all the relevant literature. Their differences in aims and scope are subtle but clear.
|Features||Systematic reviews||Scoping reviews|
|Review question||Single question with narrow parameters||Question is often broad|
|Sources||Collate empirical evidence from a relatively smaller number of studies on a focused question||Give an overview of a potentially large and diverse body of literature|
|Selection criteria||Predefined protocol-based eligibility (inclusion and exclusion) criteria||Predefined protocol-based eligibility (inclusion and exclusion) criteria|
|Data evaluation and synthesis||Critically appraised result to a question with statistical values (through meta-analysis)||Provide an overview mapping of existing evidence|
Generally, don’t assess methodological limitations or bias risks of existing evidence
|Provision of implications for practice||Provide concrete guidance for evidence-based practice and policymaking||Either don’t make implications for practice or have limited implications|
Main differences between a systematic review and a narrative review
Systematic reviews differ greatly from narrative reviews.
As seen, systematic reviews answer a narrow question through detailed and comprehensive literature searches. But narrative reviews are more descriptive. They provide authors’ subjective perspectives on a focused but broader topic.
|Features||Systematic reviews||Narrative reviews|
|Review question||Clearly defined research question||Broad overview of a general or specific topic|
|Sources||Comprehensive high-recall search for published and unpublished material|
Explicit search strategy
|Non-predefined search and collation strategy|
|Selection criteria||Predefined protocol-based eligibility criteria as per hypothesis|
Limited selection bias
Potential selection bias
|Data evaluation and synthesis||Data is extracted and appraised in a structured way|
Meta-analyses give in a pooled estimate of intervention effectiveness
|Overall description of study findings|
Qualitative summary of results
|Provision of implications for practice||Provision of concrete recommendations and implications for practice||Very limited to none|
Main differences between a scoping review and a narrative review
Scoping reviews and narrative reviews have similar differences to systematic reviews and narrative reviews. Their key difference is that narrative reviews do not follow a standardized methodology.
|Features||Scoping reviews||Narrative reviews|
|Review question||Question is often broad||Broad overview of a general or specific topic|
|Sources||Transparent search strategy informed by an a priori protocol||Subjective search and collation strategy|
|Selection criteria||Follow a rigorous and systematic process to define eligibility criteria||Subjective inclusion and exclusion criteria for primary studies|
Potential selection bias
|Data evaluation and synthesis||Offer a knowledge synthesis|
Use a more rigorous methodology to prevent bias
|Summarize literature as per the author’s preference|
Offer generally qualitative summary of results
|Provision of implications for practice||Sometimes make implications for practice (but don’t always offer concrete guidance)||Very limited to none|
Any of the above reviews is a big undertaking, and very rewarding. When you need some help in any stage of the process, we have a big range of services. We’ll connect you with publication experts to guide you through the process. Explore Edanz research services here.