Systematic review
A systematic review is a literature review
Literature review
A literature review is a body of text that aims to review the critical points of current knowledge including substantive findings as well as theoretical and methodological contributions to a particular topic...

 focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trial
Randomized controlled trial
A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...

s are crucial to evidence-based medicine
Evidence-based medicine
Evidence-based medicine or evidence-based practice aims to apply the best available evidence gained from the scientific method to clinical decision making. It seeks to assess the strength of evidence of the risks and benefits of treatments and diagnostic tests...

. An understanding of systematic reviews and how to implement them in practice is becoming mandatory for all professionals involved in the delivery of health care
Health care
Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...

. Besides health interventions, systematic reviews may concern clinical tests, public health interventions, adverse effects, and economic evaluations.

Systematic reviews are not limited to medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 and are quite common in other sciences where data are collected, published in the literature, and an assessment of methodological quality for a precisely defined subject would be helpful. Other fields where systematic reviews are used include psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

, nursing
Nursing is a healthcare profession focused on the care of individuals, families, and communities so they may attain, maintain, or recover optimal health and quality of life from conception to death....

, public health
Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...

, occupational therapy
Occupational therapy
Occupational therapy is a discipline that aims to promote health by enabling people to perform meaningful and purposeful activities. Occupational therapists work with individuals who suffer from a mentally, physically, developmentally, and/or emotionally disabling condition by utilizing treatments...

, speech therapy, physical therapy
Physical therapy
Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and rehabilitation...

, educational research
Educational research
Educational research refers to a variety of methods, in which individuals evaluate different aspects of education including but not limited to: “student learning, teaching methods, teacher training, and classroom dynamics”....

, sociology
Sociology is the study of society. It is a social science—a term with which it is sometimes synonymous—which uses various methods of empirical investigation and critical analysis to develop a body of knowledge about human social activity...

 and business management.


A systematic review aims to provide an exhaustive summary of literature relevant to a research question
Research question
A research question is the methodological point of departure of scholarly research in both the natural sciences and humanities. The research will answer any question posed...

. The first step of a systematic review is a thorough search of the literature for relevant papers. The Methodology section of the review will list the database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

s and citation index
Citation index
A citation index is a kind of bibliographic database, an index of citations between publications, allowing the user to easily establish which later documents cite which earlier documents. The first citation indices were legal citators such as Shepard's Citations...

es searched, such as Web of Science
Web of Science
ISI Web of Knowledge is an academic citation indexing and search service, which is combined with web linking and provided by Thomson Reuters. Web of Knowledge coverage encompasses the sciences, social sciences, arts and humanities. It provides bibliographic content and the tools to access, analyze,...

, Embase
Embase is an online information source of published literature designed to supportinformation managers and pharmacovigilance in complying with the regulatoryrequirements of a licensed drug. Through its unique and comprehensive content coverage,...

, and PubMed
PubMed is a free database accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez information retrieval system...

, as well as any individual journals. Next, the titles and the abstracts of the identified articles are checked against pre-determined criteria for eligibility and relevance. This list will depend on the research problem. Each paper may be assigned an objective assessment of methodological quality using the Jadad scale
Jadad scale
The Jadad scale, sometimes known as Jadad scoring or the Oxford quality scoring system, is a procedure to independently assess the methodological quality of a clinical trial...

 or similar rating system.

Systematic reviews often, but not always, use statistical techniques (meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...

) to combine results of the eligible studies, or at least use scoring of the levels of evidence depending on the methodology used. An additional rater may be consulted to resolve any scoring differences between raters. Systematic review is often applied in the biomedical
Biomedical research
Biomedical research , in general simply known as medical research, is the basic research, applied research, or translational research conducted to aid and support the body of knowledge in the field of medicine...

 or healthcare context, but it can be applied in any field of research. Groups like the Campbell Collaboration are promoting the use of systematic reviews in policy-making beyond just healthcare.

A systematic review uses an objective and transparent approach for research synthesis, with the aim of minimizing bias. While many systematic reviews are based on an explicit quantitative
Quantitative research
In the social sciences, quantitative research refers to the systematic empirical investigation of social phenomena via statistical, mathematical or computational techniques. The objective of quantitative research is to develop and employ mathematical models, theories and/or hypotheses pertaining to...

In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...

 of available data, there are also qualitative
Qualitative research
Qualitative research is a method of inquiry employed in many different academic disciplines, traditionally in the social sciences, but also in market research and further contexts. Qualitative researchers aim to gather an in-depth understanding of human behavior and the reasons that govern such...

 reviews which adhere to the standards for gathering, analyzing and reporting evidence. The EPPI-Centre
The Evidence for Policy and Practice Information and Co-ordinating Centre is part of the Social Science Research Unit at the Institute of Education, University of London...

 has been influential in developing methods for combining both qualitative and quantitative research in systematic reviews.

Recent developments in systematic reviews include realist reviews, developed by Ray Pawson
Ray Pawson
Ray Pawson is a reader of sociology at University of Leeds . His main interest lies in research methodology. He has written widely on the philosophy and practice of research, covering methods qualitative and quantitative, pure and applied, contemporaneous and historical...

 and Trisha Greenhalgh, and the meta-narrative approach by Greenhalgh and colleagues. These approaches try to overcome the problems of methodological and epistemological heterogeneity in the diverse literatures existing on some subjects. The CONSORT statement suggests a standardized way to report on parallel group randomized trials, and is now required for this kind of result by most medical journals.

Cochrane Collaboration

Many healthcare journals
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...

 now publish systematic reviews, but the best-known source is The Cochrane Collaboration, a group of over 28,000 specialists in health care who systematically review randomised trials of the effects of prevention, treatments and rehabilitation as well as health systems interventions. When appropriate, they also include the results of other types of research. Cochrane Reviews are published in The Cochrane Database of Systematic Reviews section of The Cochrane Library. The 2010 impact factor
Impact factor
The impact factor, often abbreviated IF, is a measure reflecting the average number of citations to articles published in science and social science journals. It is frequently used as a proxy for the relative importance of a journal within its field, with journals with higher impact factors deemed...

 for The Cochrane Database of Systematic Reviews was 6.186, and it was ranked 10th in the “Medicine, General & Internal” category.

The Cochrane Group provides a handbook for systematic reviewers of interventions which "provides guidance to authors for the preparation of Cochrane Intervention reviews." The Cochrane Handbook oulines eight general steps for preparing a systematic review:
  1. Defining the review question and developing criteria for including studies
  2. Searching for studies
  3. Selecting studies and collecting data
  4. Assessing risk of bias in included studies
  5. Analysing data and undertaking meta-analyses
  6. Addressing reporting biases
  7. Presenting results and "summary of findings" tables
  8. Interpreting results and drawing conclusions

Strengths and weaknesses

While systematic reviews are regarded as the strongest form of medical evidence, a review of 300 studies found that not all systematic reviews were equally reliable, and that their reporting could be improved by a universally agreed upon set of standards and guidelines.

A further study by the same group found that of 100 systematic reviews monitored, 7% needed updating at the time of publication, another 4% within a year, and another 11% within 2 years; this figure was higher in rapidly-changing fields of medicine, especially cardiovascular medicine. A 2003 study suggested that extending searches beyond major databases, perhaps into gray literature
Gray literature
Gray literature is a field in library and information science. The term is used variably by the intellectual community, librarians, and medical and research professionals to refer to a body of materials that cannot be found easily through conventional channels such as publishers, "but which is...

, would increase the effectiveness of reviews.

External links

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