The PRISMA 2020 Statement emphasizes the importance of a comprehensive search strategy when conducting a systematic review. This means searching multiple databases to ensure that all relevant literature is identified. Databases are curated collections of information—primarily scholarly articles—and are essential tools in the systematic review process. Authors must declare their sources of information and justify their selection based on the topic and scope of their review.
Journals vs. Databases
A journal is a single publication that releases peer-reviewed articles, often focusing on a specific subject area. A database, on the other hand, indexes articles from many journals, allowing researchers to search across thousands (or even millions) of articles in one place. Databases can be discipline-specific (focusing on one field) or multidisciplinary (covering many fields).
General Recommendation for Database Selection
When selecting databases for a systematic review, it’s generally recommended to include:
At least two discipline-specific databases
One multidisciplinary database
One database for grey literature
This approach helps ensure coverage of both published and unpublished studies and reduces the risk of bias.
What is Grey Literature?
Grey literature includes research that is not formally published in books or peer-reviewed journals. Examples include:
Government or NGO reports
Conference papers
Dissertations and theses
Policy briefs
Technical documents
Grey literature is valuable because it often contains important data that may not be published elsewhere.
What is Publication Bias?
Publication bias occurs when studies with positive or significant findings are more likely to be published than those with negative or inconclusive results. This skews the evidence base and can mislead systematic reviews. Including grey literature is a key strategy for mitigating publication bias.
Accessing Databases
Most high-quality academic databases require institutional access—usually via universities, research institutions, or healthcare organizations. Individual subscriptions are rarely available due to cost and licensing restrictions. Universities typically subscribe based on their academic programs, but access may be limited, especially in middle- and low-income countries.
Access in Middle- and Low-Income Countries
For those in eligible low- and middle-income countries, the HINARI program, offered by Research4Life and coordinated by the World Health Organization (WHO), provides free access to many scientific databases. Institutions such as universities, colleges, public hospitals, government offices, and national libraries can register. If an institution is not already a member, an administrator can apply—it's free, though the process may take some time.
Access in High-Income Countries
Researchers in high-income countries should check with their institution—university, research center, or hospital—to find out which databases are available to them.
Barrier Alert: One of the biggest obstacles to conducting rigorous systematic reviews is lack of access to premium databases.
Commonly Used Databases (Grouped by Discipline)
Multidisciplinary Databases
Scopus
Covers science, technology, medicine, social sciences, and humanities. Requires institutional access. Owned by Elsevier.Web of Science
Broad coverage of academic disciplines, strong for citation tracking. Institutional access required. Managed by Clarivate Analytics.Academic Search Complete (via EBSCOhost)
Covers a wide range of disciplines. Institutional access required.Google Scholar
Free to use. Covers all disciplines and includes grey literature. Helps mitigate publication bias.
Healthcare and Social Sciences
PubMed
Free resource covering biomedicine and life sciences. Maintained by the U.S. National Library of Medicine.MEDLINE
Subset of PubMed. Core biomedical literature. Free via PubMed; institutional access needed for Ovid version.CINAHL
Nursing and allied health. Requires institutional access. Available via EBSCOhost.PsycINFO
Psychology and behavioral sciences. Requires institutional access. Managed by APA.Cochrane Central Register of Controlled Trials (CENTRAL)
Important for clinical trials. Requires institutional access. Part of the Cochrane Library (Wiley).EMBASE
Biomedical and pharmaceutical research. Especially strong in drug studies. Requires institutional access. Owned by Elsevier.LILACS
Focuses on Latin American and Caribbean health literature. Free to access.ProQuest Dissertations & Theses Global
Offers access to theses and dissertations. Valuable for grey literature. Requires institutional access.Sociological Abstracts
Literature in sociology and social sciences. Requires institutional access. Available through ProQuest.
Engineering, Technology, and Natural Sciences
IEEE Xplore
Electrical engineering, computer science, and electronics. Institutional access required.ScienceDirect
Journals in science, technology, and medicine. Requires institutional access. Owned by Elsevier.INSPEC
Focuses on physics, electrical engineering, and computing. Institutional access needed. Managed by IET.ACM Digital Library
Computing and information technology. Requires institutional access. Provided by ACM.AGRIS
Agriculture and food science. Free access. Managed by the Food and Agriculture Organization (FAO).GreenFILE
Environment and sustainability topics. May require institutional access. Available via EBSCOhost.
Conclusion
Selecting the right databases for your systematic review is critical. Use a blend of:
Discipline-specific databases
Multidisciplinary databases
Grey literature sources
This combination ensures your review is comprehensive and minimizes publication bias. While access can be a barrier—especially in resource-limited settings—programs like HINARI and tools like Google Scholar offer alternative routes to quality information.
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