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Systematic reviews

A brief overview of systematic reviews and resources to support producing one.

What is a systematic review?

"Systematic reviews aim to identify, evaluate and summarise the findings of all relevant individual studies, thereby making the available evidence more accessible to decisionmakers. When appropriate, combining the results of several studies gives a more reliable and precise estimate of an intervention’s effectiveness than one study alone." 

Centre for Reviews and Dissemination. Systematic Reviews: CRD's guidance for undertaking reviews in health care. York (GB): Centre for Reviews and Dissemination; 2009.

A systematic review is a review that reports or includes the following:

  • research question
  • sources that were searched, with a reproducible search strategy (naming of databases, naming of search platforms/engines, search date and complete search strategy)
  • inclusion and exclusion criteria
  • selection (screening) methods
  • critically appraises and reports the quality/risk of bias of the included studies
  • information about data analysis and synthesis that allows the reproducibility of the results

Krnic Martinic M, Pieper D, Glatt A, Puljak L. Definition of a systematic review used in overviews of systematic reviews, meta-epidemiological studies and textbooks. BMC Med Res Methodol. 2019;19(1):203.

Identifying the need for a systematic review

The reasons for a systematic review may include:

  • Uncertainty in the research literature where there are conflicting results
  • An identified gap in knowledge
  • An area in which research and interest are growing
  • To prove effectiveness

Watch: Features and benefits of a systematic review (YouTube, 1m 49s)

Part of establishing the need for your planned systematic review is to check that a systematic review doesn't already exist for your topic. See the section of this guide 'Finding existing systematic reviews'.

Types of systematic reviews

Systematic reviews have a focused answerable question often developed and defined by a PICO statement. Systematic and transparent methods must be used and reported which enable repeatability and eliminate bias. A rigorous and sensitive search strategy should be developed to attempt to find all published and unpublished relevant literature. Studies for analysis should be chosen using clear, pre-determined inclusion/exclusion criteria. Selected studies should be appraised and all relevant data analysed with the results used to drive policy and practice.

Meta-analysis and systematic review have, in the past, been used interchangeably, however meta-analysis (or meta-synthesis for qualitative research) is now more often used to describe the data analysis that takes place within the systematic review process.

Rapid reviews aim to use the methodology of the systematic review but where a systematic review may take 18 months results may be expected in 6 to 8 weeks. Generally, an effective rapid review requires more subject knowledge and understanding of the systematic review process of the reviewers than does a systematic review. To achieve best results, given the time constraints reviewers could chose to interrogate fewer databases, perhaps 3 as opposed to the 7 or more used in the typical systematic review. Grey literature may not be included and the screening process may be undertaken by a single reviewer after a benchmarking search involving more reviewers looks at a small percentage of the papers to be screened. The aim of a rapid review is to quickly translate findings to policy and practice.

State of the art reviews are very similar to systematic reviews but are interested only in very recent research, more often in emerging areas.

Umbrella reviews undertake much the same process as systematic reviews, however no primary studies are considered, they are reviews of reviews. The aims are the same as systematic reviews, to influence policy and practice but they have the capacity to do so for a broader concept.

Other reviews

Literature reviews (narrative, critical) have been with us as long as literature and generally seek to find a subset of papers in a selected area and summarise them. 

Scoping reviews, as far as searching, reporting and study selection are concerned, can be much the same as systematic reviews. The question may be much broader than that of a systematic review often considering concepts rather than focused questions. The final analysis and goals of the scoping review are the fundamental differences between scoping and systematic reviews. Charting is the term most often used to describe the “analysis” of the results of a scoping review. The scope or reach of the concept is charted perhaps geographically, socially, temporally or other respects. A scoping review can determine whether a systematic review on the topic is warranted or viable.

Systematic quantitative literature review. This method developed by Griffith University's School of Environment bridges the gap between traditional narrative review methods and meta-analyses.

Systematised literature review. This method attempts to include elements of the systematic review process while stopping short of the systematic review. Systematised reviews are typically conducted as a postgraduate student assignment, in recognition that they are not able to draw upon the resources required for a full systematic review (such as two reviewers).

Literature review vs systematic review

Systematic reviews are very different to narrative (literature) reviews. The list below highlights some of the principle features which set systematic and narrative reviews apart.

Systematic Review

  • Has a clear question or hypothesis to be answered
  • Searches are rigorous to locate all potentially relevant literature
  • Includes explicit inclusion and exclusion criteria
  • Assesses study quality for inclusion and provides a synthesis of results

Narrative (Traditional) Review

  • Starts with a question but includes general discussion and no hypothesis
  • Does not locate all relevant literature
  • Does not have explicit inclusion and exclusion criteria
  • Does not always require included studies to be methodologically sound or of a certain quality

Mark, P. Systematic reviews from astronomy to zoology: myths and misconceptions. BMJ. 2001;322(7278):98-101.

For more information on how to search for, store, organise, evaluate and critique information for your literature review (any type) see our Literature reviews guide. Includes techniques, books, articles and more to help you do your literature review. If your project requires a systematic approach then the information in this guide (Systematic Reviews) may be the most helpful.