What is a literature review?
Research is based on existing knowledge and is expected to fill knowledge gaps. Therefore, any research project begins with or is based on a literature review. A literature review aims to summarize, combine, analyze, comment or critique existing publications on a given topic. Literature reviews represent a large portion of published scientific articles, which are consulted by the scientific and non-scientific communities.
Main types of literature reviews
There are two main types of reviews: traditional and systematic.
Traditional review
Traditionally, the methods used in literature reviews were not always clearly explained or reported in detail. Such reviews were criticized for their lack of objectivity and scientific rigour. For example, only a few studies on a given topic are identified, the selection of studies seems arbitrary (without clear selection criteria), and the analysis of studies can be influenced by the researcher’s preconceptions.
To increase scientific rigour, researchers have been interested in developing methods to make the review process more rigorous. In the “traditional” review there is generally no method described and therefore, it cannot be reproduced. Various terms are used to describe this type of review, for example, simply “literature review” or “critical review”.
Systematic review
At the other extreme, there is systematic review, which is one of the most rigorous types of review. Here, the method is clear and various strategies are used to increase scientific rigour. Systematic reviews are used to enable decision-making based on the best available evidence.
A systematic review is a type of literature review that uses explicit and systematic methods to identify, select, evaluate and analyze studies in order to answer a specific review question. For example, researchers will search in different databases and other sources to ensure that they find all potentially relevant studies. There will be very clear selection criteria. Two people (independent reviewers) will be involved in all stages of the review to avoid possible selection bias.
Characteristics of a systematic review:
- transparent
- reproducible
- explicit
- comprehensive/exhaustive
Other types of reviews
Rapid review
Review produced for decision-makers that need an answer quickly; may simplify or omit certain steps of the systematic review
Umbrella review
(also named review of reviews)
Review that analyzes multiple systematic reviews
Scoping review
Review that evaluates the extent of knowledge on a given topic, how much literature exists and the characteristics of that literature
Additional resources
- What are systematic reviews?: a video from Cochrane explaining why systematic reviews are important and how they are done.
- Types of Reviews What kind of review do we need?
- Forest Plots: Understanding a Meta-Analysis in 5 Minutes or Less
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