Review purpose
Traditional literature reviews are designed to provide a broad overview or increase self-knowledge of an area of specialisation. They may also provide background to a research thesis.
Recommended time frame
1+ week
Reviewers required
1 or more
Example review
Smoking Cessation for People Living With HIV/AIDS: A Literature Review and Synthesis
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Traditional literature reviews (also known as narrative reviews) are unlikely to be published as stand-alone pieces of work. Instead, they provide context for subsequent work and form a smaller part of a larger piece. Literature reviews function well as a topic overview for readers by succinctly outlining the area of research development.
Authors can select and appraise papers subjectively, without predetermined criteria. The search method or strategy for identifying the papers included in the review is often ambiguous or left unexplained.
A traditional review can be completed in as little as a week depending on the scope of the review.
Review purpose
Scoping reviews comprehensively summarise evidence to inform practice, programs and policy. Scoping reviews explore and establish overall themes or determine the extent of available evidence.
Recommended time frame
2-6 months
Reviewers required
1 or more
Example review
Tobacco use cessation interventions for lesbian, gay, bisexual, transgender and queer youth and young adults: A scoping review.
More information
Scoping reviews are interested in broader questions and understanding 'what is known' about a topic. Scoping reviews can be undertaken as a stand-alone project, especially where an area is complex or has not been reviewed in depth previously. This makes them particularly useful for an emerging health area or to determine if a systematic review is therefore required.
Search strategies for scoping reviews are still expected to be systematic, transparent and replicable. A key difference to systematic reviews is the absence of a critical appraisal stage.
The lack of study appraisal in scoping reviews means they can be conducted with a single author. However, multiple reviewers will reduce bias in the study selection stage.
Review purpose
Rapid reviews seek to synthesise research evidence with minimal bias to assist with best practices.
Recommended time frame
2 – 6 months
Reviewers required
2 or more
Example review
Cost-Effectiveness of Lifestyle-Related Interventions for the Primary Prevention of Breast Cancer: A Rapid Review
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Rapid reviews (also known as rapid evidence assessment) are often conducted in response to:
- requests from policymakers that are time-sensitive
- constraints on finances or other resources
Rapid reviews use similar methods to systematic reviews but are less comprehensive and are completed in a much shorter time frame (e.g. two to six months). Searching is systematic and transparent, but less exhaustive than a systematic or integrative review.
Some aspects of the systematic review process are omitted or shortened to enable shorter timeframes. This could involve one or more of the following:
- Searching a smaller selection of databases
- Omitting grey literature and/or hand searching
- Restricting to a particular study type
- Reviewing reviews
- Limiting the number of outcomes being included
- Quality assessed at study design level, rather than appraising individual studies
- Limiting the amount of analysis and interpretation
The details of steps omitted in the rapid review process will be listed in the article, often in the limitations section, (see ‘The rollercoaster of follow-up care’ after bariatric surgery: a rapid review and qualitative synthesis).
Review purpose
Systematic reviews aim to find, evaluate and combine elements from all available evidence, in relation to a specific and focused question. Often systematic reviews compare actions (such as interventions) to decide which is the most effective, although they not limited to that purpose.
Recommended time frame
6 months – 2 years
Reviewers required
At least 2 or more
Example review
Internet-based interventions for smoking cessation
More information
Systematic reviews are concerned with reducing bias in the review process. As such, they typically include these features:
- Pre-determined selection criteria, and methods for research appraisal and data synthesis, published with other details as a protocol prior to commencing the review 'proper'.
- Resources gathered from search strategies undergo a selection process to determine the quality of the study (e.g., biases and study data) which are included in the final review.
- Systematic reviews should be conducted with two or more people involved in the study selection and appraisal stages.
Notably, the work of finding available evidence requires an effective, transparent and reproducible search strategy. The search strategy typically tends to lean towards sensitivity, a high number of search results. This is at the expense of precision, as the proportion of those search results that are subsequently relevant to the review question.
Review purpose
Mixed methods reviews have multiple questions or several aspects to their research question to provide a more in-depth picture of the issue. A mixed methods review may look to determine both the effect of an action (intervention) and when that action is clinically appropriate, which usually requires multiple searches, and quantitative and qualitative research data, to address subtopics.
Recommended time frame
12 – 18+ months
Reviewers required
Large review team
Example reviews
More information
Mixed methods reviews (also known as Mixed-methods systematic reviews) are best suited to:
- topics that are multidisciplinary or
- topics with a body of literature
Mixed method reviews usually include evidence or data from quantitative, qualitative, and mixed methods studies, in order to produce meaningful connections around a topic.
A distinguishing feature of mixed method reviews is that the exact question may be broad in nature. This means that the planning phase will be long as you will be required to gather a lot of resources.
Questions or hypotheses may emerge throughout a mixed method review. Therefore, protocols for your review will generally be developed over time, rather than in a predetermined manner.
There are currently no universally adopted methods for conducting mixed methods reviews. As these reviews are highly repetitive in nature, meaning they are less transparent and not inherently reproducible.
Review purpose
Umbrella reviews are essentially systematic reviews of existing reviews. Their aim is to focus on broad conditions or problems, for which there are competing interests, and to reduce duplication.
Recommended time frame
3-6 months
Reviewers required
At least 2 or more
Example review
Environmental risk factors for inflammatory bowel diseases: an umbrella review of meta-analyses
More information
Umbrella reviews (known as the "review of reviews") have a broader focus than a systematic review. They aim to locate and summarise all the evidence from research syntheses related to a topic or question.
This evidence informs guidelines and clinical practice by:
- considering different treatment or management options for the same condition
- examining the same intervention and condition, but with different outcomes
- evaluate the same intervention but when applied to a different condition, situation or population
Each comparison is considered separately and used to summarise or synthesise the findings. Where appropriate meta-analyses are performed. Umbrella reviews are most useful where an area has been researched extensively.
Often, umbrella reviews will use only systematic reviews as the eligible study type.
Generally, there is no search for primary studies and there is an expectation of multiple authors to reduce bias.
Review purpose
Integrative reviews aggregate experimental data, non-experimental data and theoretical information into a combined synthesis in order to answer specific questions.
Recommended time frame
12+ months
Reviewers required
2 or more
Example review
Passive interventions in primary healthcare waiting rooms are effective in promoting healthy lifestyle behaviours: an integrative review.
More information
Integrative reviews can be useful for informing policy and practice, and for developing theory. Because of the complexity inherent, expect an integrative review to take more than 12 months with a team of at least two reviewers.
The pool of eligible studies for an integrative review is much larger than for a systematic review exploring a similar area.
The search strategy for an integrative review should aim to be exhaustive and systematic. Reporting of the search strategy is required for transparency.
