In science, literature reviews are studies which:
There are many types of literature review, but two of the main ones are:
The image at above right describes common review types in terms of speed, detail, risk of bias and comprehensiveness.
For more details, see CSU's Library Resource Guides for researchers on
[Image attribution: "Schematic of the main differences between the types of literature review" by Brennan, M. L., Arlt, S. P., Belshaw, Z., Buckley, L., Corah, L., Doit, H., Fajt, V. R., Grindlay, D., Moberly, H. K., Morrow, L. D., Stavisky, J., & White, C. (2020). Critically Appraised Topics (CATs) in veterinary medicine: Applying evidence in clinical practice. Frontiers in Veterinary Science, 7, 314. https://doi.org/10.3389/fvets.2020.00314 is licensed under CC BY 3.0.]
A narrative review of the literature provides an overview of the research on a given topic, but usually lacks systematic search protocols or clear criteria for selecting and appraising evidence. They are often qualitative in approach and can be prone to bias.
Photo credit: Urval av de Bocker sum var hunnit Nordisk radets litteraturpris under de 50 ar som priset funnits (3) by Johannes Jansson/norden.org. Licensed under CC BY 2.5 dk via Commons.
A systematic review is just that: a systematic review of the literature on a certain topic or to answer a clinical question. Reviewers carry out an extensive search of the literature to identify studies that have sound methodology. They use rigorous, systematic, and documented methods to review and assess the studies for quality, and to pool and summarise the results.
Systematic reviews are not necessarily the highest level of evidence, but they have the advantage of drawing together a number of studies and compiling the results.
A systematic review will often include a meta-analysis. This is where data from a number of valid studies are combined mathematically and then reported as if from a single study.
The best-known source of systematic reviews (for healthcare) is the Cochrane Library's Cochrane Database of Systematic Reviews. Here's how the Cochrane Library defines a systematic review:
"A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform decision making."
[ from https://www.cochranelibrary.com/about/about-cochrane-systematic-reviews.html ]
See also the More Resources on Systematic Reviews box below for the Cochrane Library's full definition of a systematic review.
Some databases are specific for evidence-based practice material and provide synopses (summaries) of systematic reviews. If you do not have time to look at a detailed systematic review, then a synopsis which summarises the findings of a systematic review might suffice. The synopsis often also has a commentary on the methodological quality and clinical applicability of the review:
Other evidence-based practice databases are excellent sources of systematic reviews:
You can also search the major health/medical databases for systematic reviews. Some databases have specific limiters for systematic reviews:
If your research or topic is cross-disciplinary, you might benefit from searching in one of the large citation indexes: