Systematic Reviews (A How-To Guide): What is a Systematic Review?

Scope & Definitions

A systematic review is a particular type of evidence synthesis whose methodology seeks to maximize objectivity and transparency while minimizing bias in the identification, evaluation and use of information used to support an answer to a research question. Here below are some ways different authors have described the systematic review approach:

"A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question. Researchers conducting systematic reviews use explicit, systematic methods that are selected with a view aimed at minimizing bias, to produce more reliable findings to inform decision making" (Cochrane Library website: About Cochrane Reviews, 2022)

“a review of existing research using explicitly, accountable rigorous research methods”  (Gough, Oliver & Thomas, 2017)

“a set of transparent, orderly, structurally interrelated steps, carried out in a way that avoids bias and allows for peer review and independent verification. The SR addresses a clearly defined question. It uses a systematic, that is, logical, and explicit methodology to identify, select, and critically appraise relevant studies”  (Holly, Salmond & Saimbert, 2022)

“a particular form of secondary study and aims to provide an objective and unbiased approach to finding relevant primary studies, and for extracting, aggregating and synthesizing the data from these.” (Kitchenham, Budgen & Brereton, 2016)

Methodologies (Variations & Options)

The details of systematic review methodology may vary across different fields of study, including, but not limited to: medicine, nursing, psychology, education, the social sciences, and increasingly in the fields of engineering and software development.

Other determining factors for the systematic review methodology include: the nature of the information sources being used; the type of information collected; the specificity of the research question; the breadth or narrowness of the inclusion criteria, exclusion criteria and search strategy; and the particular research goals of the investigators (for additional guidance, refer to the "Further Reading & Guidance" section of this guide).

One of the most important variations on systematic review methodology is the 'meta-analysis'--a type of evidence synthesis that includes statistical analysis of information collected from multiple independent studies (e.g. from different clinical trials).

Systematic reviews may be published and disseminated in the form of journal articles, book chapters, graduate theses and dissertations, technical reports, conference proceedings, and other document types.

Defining Characteristics

The main attributes that systematic reviews have in common include:

• The goal of answering a clearly stated, predefined and focused research question
• The use of explicit predetermined criteria for determining the eligibility of information sources
• A systematized methodology and protocol that seek to maximize objectivity and minimize bias in the identification, selection and use of relevant information sources
• Exhaustive (comprehensive and thorough) searches that attempt to find all available information that could help support an answer to the predefined research question
• Rigorous evaluation of search results according to predefined quality criteria
• Reproducibility through transparency in reporting of all methods, results, and evaluation processes
• An overall time commitment of between six months to a year or more
• A project team of three or more people with appropriate subject expertise

If your goals or resources are not consistent with those listed above, a different review methodology may be a better fit for your project. Other evidence synthesis methodologies to consider may include: rapid review, scoping review, narrative literature review, or a methodology that incorporates elements of a systematic review approach but a lesser degree of rigor or exhaustiveness (see the "Planning & Logistics" section of this guide).

Explore Your Options with a Librarian

If in any doubt about the appropriateness of a systematic review methodology--or any other type of knowledge synthesis--for meeting your research goals, feel encouraged to discuss options with a librarian (bring along any collaborators and/or instructors in your project team).

Before embarking on your project, here below is a decision-support tool offering guidance as to the appropriateness of the systematic review methodology for fulfilling your particular research goals:

What kind of review is right for you?

(Cornell University Library)