A systematic review is a type of secondary evidence that summarises research that has already been published.

Systematic reviews, according to Wright, et al., are defined as a:

“review of the evidence on a clearly formulated question that uses systematic and explicit methods to identify, select and critically appraise relevant primary research, and to extract and analyze data from the studies that are included in the review.”

What are Systematic Reviews? (3:23 min) by Cochrane (YouTube)

When conducting a systematic review it is important to ask a question that can be answered through use of evidence, rather than subjective judgment. In evidence based practice, systematic reviews are considered one of the highest levels of information.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters (pdf) by Lynn Kysh / CC-BY 4.0

A systematic review may sometimes include a meta-analysis. A meta-analysis is the use of statistical methods to combine data from studies included in a systematic review. Not all systematic reviews include a meta-analysis.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters (pdf) by Lynn Kysh / CC-BY 4.0

A systematic review is a type of literature review. The differences between a systematic review and a literature review are outlined in the following table.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters (pdf) by Lynn Kysh / CC-BY 4.0

There are a number of different types of reviews, following is a brief description of some review types.

1. Literature review - A literature review, also known as a narrative review, is the most common review type. Generally, it provides an examination of current literature of a topic area. The completeness and comprehensiveness of the literature included is subjective. Searches are usually limited and do not include quality assessment of the material. Typically, the synthesis is narrative, and analysis may be chronological, conceptual, thematic, etc. The library guide Literature reviews provides guidance on starting a literature review, including resources, techniques and approaches to searching the literature and writing the review.
    
2. Systematic review - A systematic review seeks to systematically search for, appraise, and synthesise research evidence, adhering to guidelines on the conduct of a review. Aims for exhaustive, comprehensive searching. Quality assessment is carried out. Typically, narrative with tabular accompaniment. Synthesis outlines what is known and recommendations for practice, as well as recommendations for future research. The library guide Systematic reviews outlines the process for conducting a systematic review.
    
3. Meta-analysis - A meta-analysis is a technique that statistically combines the results of quantitative studies to provide a more precise effect of the results. Aims for exhaustive, comprehensive searching. May use a funnel plot to assess completeness. Quality assessment is carried out. Synthesis is graphical and tabular with narrative commentary. Numerical analysis of measures of effect are provided. The library guide Systematic reviews briefly refers to meta-analyses.
    
4. Scoping review - A scoping review is a preliminary assessment of potential size and scope of available research literature. Aims to identify the nature and extent of research evidence by characterising quantity and quality of literature, perhaps by study design. Completeness of searching determined by time/scope constraints. No formal quality assessment is carried out. Synthesis is typically tabular with some narrative commentary. Attempts to specify a viable review.
    
5. Rapid review - A rapid review is an assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research. Completeness of searching determined by time constraints. Time‐limited formal quality assessment. Synthesis is typically tabular with some narrative commentary.

Further reading

Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26(2), 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x

Paré, G., Trudel, M.-C., Jaana, M., & Kitsiou, S. (2015). Synthesizing information systems knowledge: A typology of literature reviews. Information & Management, 52(2), 183-199. https://doi.org/10.1016/j.im.2014.08.008