Search Databases for Systematic Reviews: A Comprehensive Overview

Systematic reviews are a cornerstone of evidence-based research, providing a rigorous and unbiased synthesis of existing literature to answer specific research questions. These reviews are widely used across diverse fields, from healthcare and social sciences to engineering and beyond, playing a crucial role in informing decision-making, shaping policies, and guiding future research directions 1. Given the comprehensive nature of systematic reviews, employing appropriate search databases is paramount to ensure the identification of all relevant literature. This article offers a detailed overview of commonly used search databases for systematic reviews, comparing their features, strengths, and limitations to aid researchers in selecting the most suitable resources for their specific needs. Moreover, it emphasizes the importance of adhering to established guidelines, such as those outlined in the Cochrane Handbook, for conducting thorough and reliable systematic reviews 2.

Commonly Used Search Databases for Systematic Reviews

The selection of databases for a systematic review hinges on the specific research question and the field of study. While a plethora of databases exist, some of the most frequently utilized for systematic reviews include:

• MEDLINE: A cornerstone of biomedical research, MEDLINE is compiled by the United States National Library of Medicine (NLM) and offers extensive coverage of life sciences literature, with a particular focus on biomedicine. Encompassing a wide array of publications, including journal articles, newspapers, magazines, and newsletters, MEDLINE primarily caters to the needs of health professionals. Its historical coverage spans from 1809 to the present, encompassing citations from over 5,600 journals worldwide in approximately 40 languages 3. A distinctive feature of MEDLINE is its use of NLM Medical Subject Headings (MeSH) for indexing, which facilitates precise and efficient retrieval of biomedical information 4. Furthermore, MEDLINE Complete offers full-text access to numerous popular MEDLINE-indexed journals not available in other databases, enhancing its value for researchers 6.
• PubMed: Developed and maintained by the National Center for Biotechnology Information (NCBI) at the US National Library of Medicine (NLM), PubMed is a freely accessible resource that provides a gateway to a vast collection of biomedical literature. In addition to encompassing all MEDLINE citations, PubMed includes content from life science journals and online books, covering a broad spectrum of fields, including life sciences, behavioral sciences, chemical sciences, and bioengineering 7.
• Embase: Produced by Elsevier B.V., Embase is a comprehensive biomedical and pharmacological database with extensive coverage of literature dating back to 1947 8. It offers access to over 8,400 journals from across the globe, encompassing over 30 million records, including a substantial number of conference abstracts and European journal titles not found in MEDLINE 8. Embase employs a specialized controlled vocabulary called Emtree, which provides more granular subject headings than PubMed's MeSH, enabling more precise retrieval of information, particularly in the areas of drug and pharmacology research, where Embase has particularly strong coverage 8. Additionally, Embase provides access to article preprints from MedRXiv and BioRXiv, allowing researchers to stay abreast of the latest findings 10.
• Cochrane Library: Widely regarded as the gold standard for clinical systematic reviews, the Cochrane Library is a collection of databases that provides high-quality, evidence-based healthcare information 11. It comprises the Cochrane Database of Systematic Reviews (CDSR), Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Clinical Answers 7. Cochrane CENTRAL, a vital component of the Cochrane Library, employs a comprehensive approach to identify reports of randomized controlled trials (RCTs), utilizing a combination of direct feeds, sensitive searches, machine learning, and crowdsourcing through Cochrane Crowd 12.
• Scopus: As the largest abstract and citation database of research literature and quality web sources, Scopus plays a pivotal role in academic research 2. It encompasses a vast collection of records from over 25,000 titles, including peer-reviewed journals, books, and conference proceedings, covering a wide range of disciplines 13. Scopus offers advanced search capabilities, author and affiliation profiling, citation monitoring, journal rating, metric analysis, and visualization tools 13. While Scopus and Embase are distinct databases, they may have some overlap in their coverage of biomedical literature.
• Web of Science: A comprehensive platform for accessing citation indexes, Web of Science provides access to a vast collection of scholarly literature across diverse disciplines 1. It includes the Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Book Citation Index, and Conference Proceedings Citation Index 7. Web of Science offers advanced search capabilities, author and affiliation profiling, and citation monitoring, enabling researchers to track the impact and influence of research publications 13.

Key Features of Search Databases

Selecting the most appropriate search database for a systematic review requires careful consideration of several key features:

Coverage

• Subject areas: Databases vary significantly in their subject coverage. Some, like MEDLINE and Embase, primarily focus on biomedical and healthcare literature, while others, such as Scopus and Web of Science, offer a broader multidisciplinary scope.
• Types of publications: The types of publications included in a database can range from journal articles and books to conference proceedings and grey literature, such as reports, theses, and dissertations.
• Date range: The date range of coverage is another crucial factor, with some databases offering historical coverage spanning several decades, while others concentrate on more recent publications.

Search Functionality

• Advanced search operators: To facilitate precise and efficient retrieval of relevant information, databases offer a variety of search operators, including Boolean operators (AND, OR, NOT), wildcards (e.g., *), and proximity operators (e.g., NEAR).
• Field searching: Field searching allows users to restrict their searches to specific fields within a record, such as title, author, abstract, or keywords, enhancing the precision of search results.
• Citation searching: Citation searching enables users to identify articles that cite a specific publication, which can be invaluable for uncovering relevant literature and tracing the evolution of research on a particular topic.
• Filtering options: Databases offer various filtering options, such as publication date, language, and publication type, to help users refine their search results and focus on the most relevant materials.

User Interface

• Ease of use: An intuitive and user-friendly interface is essential, particularly for novice users, to ensure efficient navigation and effective use of the database.
• Navigation: Clear and well-organized navigation options are crucial for enabling users to browse and search for information effectively.
• Customization options: Some databases offer customization features, such as saving search strategies, setting up email alerts for new publications, and creating personal accounts to manage search history and preferences.

Access and Cost

• Subscription options: Most databases operate on a subscription basis, with various options available depending on the institution or individual user needs.
• Free access options: Some databases, such as PubMed, provide free access to their content, making them valuable resources for researchers with limited funding.
• Pricing: Subscription costs vary widely depending on the database, the range of features offered, and the type of subscription chosen.

Unique Features or Strengths

• Specialized content: Certain databases specialize in specific subject areas or types of publications, such as the Cochrane Library for systematic reviews in healthcare, catering to the unique needs of researchers in those fields.
• Tools for managing search results: Many databases offer tools to help users manage their search results, including options for saving searches, exporting citations in various formats, and generating bibliographies.
• Integration with other software: Some databases integrate with other research tools, such as citation management software (e.g., EndNote, Zotero) or systematic review software (e.g., Covidence, Rayyan), streamlining the research workflow.

Detailed Comparison of Database Features

In addition to the table above, a more detailed comparison of the databases based on their key features can provide further insights for researchers:

• Coverage: MEDLINE and PubMed excel in their coverage of biomedical literature, while Embase offers broader coverage of pharmacological research and medical devices. Scopus and Web of Science provide the most extensive multidisciplinary coverage, encompassing a wide range of subject areas2.
• Search Functionality: All the databases offer advanced search functionalities, including Boolean operators, wildcards, and field searching. However, MEDLINE and PubMed leverage the MeSH thesaurus for precise indexing, while Embase utilizes the Emtree thesaurus for more granular subject headings. Scopus and Web of Science stand out for their citation tracking capabilities, allowing researchers to explore the impact and influence of publications2.
• User Interface: All the databases generally offer user-friendly interfaces with intuitive navigation. However, some, like Web of Science, provide more customization options, allowing users to tailor the interface to their specific needs2.
• Access and Cost: While PubMed offers free access, most other databases require a subscription. The cost of access varies depending on the database and the institution's subscription model2.
• Unique Features: MEDLINE's strength lies in its comprehensive coverage of biomedical literature and its use of MeSH indexing. Embase excels in its coverage of drug and pharmacology research and its detailed Emtree thesaurus. The Cochrane Library is renowned for its focus on high-quality systematic reviews in healthcare. Scopus stands out as the largest abstract and citation database, while Web of Science provides comprehensive citation indexing and tools for analyzing research impact2.

Recommendations for Choosing Databases

The selection of databases for a systematic review should be guided by the specific research question and the field of study. Here are some general recommendations:

• Medicine: For systematic reviews in medicine, the core databases recommended are MEDLINE (accessed via Ovid or PubMed), Embase, and Cochrane CENTRAL 1.
• Social Sciences: In the social sciences, researchers should consider databases like PsycINFO, which covers professional and academic literature in psychology and related disciplines 1, Sociological Abstracts, and ERIC, in addition to broader databases like Scopus or Web of Science 15.
• Engineering: For engineering, relevant databases include IEEE Xplore, Compendex, and Inspec, along with multidisciplinary databases like Scopus or Web of Science 16.

It is crucial to remember that even when platforms allow searching across multiple databases, each database should be searched individually for a systematic review to ensure comprehensiveness 1.

While selecting the right databases is crucial, it's equally important to stay updated on the latest developments in these resources.

Recent Updates and Changes

Databases are constantly evolving, with new features and updates being released regularly. Staying informed about these changes is essential to ensure that search strategies remain comprehensive and up-to-date. Some recent updates include:

• MEDLINE: The MeSH vocabulary is updated annually. In 2023, 277 new MeSH descriptors and 218 new MeSH Supplementary Concept Records were added 17.
• Embase: The Emtree thesaurus is also updated regularly. The May 2023 update included 183 new drug terms and 374 non-drug terms, further enhancing the granularity and precision of Embase's indexing 18.
• Cochrane CENTRAL: Cochrane CENTRAL is updated monthly with new records and updates to existing records. The December 2024 update added over 14,000 new records and updated over 8,000 existing records 19.
• Scopus: Scopus has introduced Scopus AI in May 2024, incorporating new features such as concept map relationships, an enhanced SML reranker for improved search precision, and a reflection layer to provide context and transparency about the AI's confidence in its responses 20. Furthermore, Scopus has removed the "2-year" publication history condition for newly launched journals, making newer research more readily accessible 21.

Conclusion

Systematic reviews demand a meticulous and comprehensive search of the literature to ensure that all relevant studies are identified and synthesized. Selecting appropriate search databases is a critical step in this process, and researchers must carefully consider the features, strengths, and limitations of different databases to make informed decisions. The choice of databases should be guided by the specific research question and the field of study, with core databases like MEDLINE, Embase, and Cochrane CENTRAL recommended for medicine; PsycINFO, Sociological Abstracts, and ERIC for social sciences; and IEEE Xplore, Compendex, and Inspec for engineering. However, it is essential to consult with a librarian or information specialist to determine the most suitable databases and develop a comprehensive search strategy tailored to the specific needs of the systematic review 15. This collaborative approach ensures that the systematic review is based on the best available evidence and adheres to established guidelines for rigor and transparency.

Works cited

1. Where to search - Systematic Reviews - Research Guide - Support - Murdoch University, accessed on January 16, 2025, https://libguides.murdoch.edu.au/systematic/databases

2. Systematic Reviews in Health: Database Searching - UC Library Guides - LibGuides, accessed on January 16, 2025, https://canberra.libguides.com/systematic/search

3. MEDLINE- Database - Health Resources - Research Guides at Louisiana State University, accessed on January 16, 2025, https://guides.lib.lsu.edu/c.php?g=727379&p=5193308

4. MEDLINE, accessed on January 16, 2025, https://www.lkouniv.ac.in/site/writereaddata/siteContent/202004061923053021rakhi_libsc_MEDLINE.pdf

5. MEDLINE Overview - National Library of Medicine, accessed on January 16, 2025, https://www.nlm.nih.gov/medline/medline_overview.html

6. MEDLINE Complete - PMC - PubMed Central, accessed on January 16, 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC4279943/

7. Core Databases - Writing Systematic Reviews for the Health and ..., accessed on January 16, 2025, https://research.library.gsu.edu/c.php?g=115802&p=751730

8. Embase - Database Search Tips - LibGuides at Duke University Medical Center, accessed on January 16, 2025, https://guides.mclibrary.duke.edu/searchtips/embase

9. Embase Help Guide: Home - Library Guides - University of Washington, accessed on January 16, 2025, https://guides.lib.uw.edu/embase

10. Embase - Becker Medical Library - Washington University, accessed on January 16, 2025, https://becker.wustl.edu/news/tag/embase/

11. Systematic Reviews and Evidence Syntheses: Databases - Research Subject Guides, accessed on January 16, 2025, https://subjectguides.lib.neu.edu/systematicreview/databases

12. How CENTRAL is created - Cochrane Library, accessed on January 16, 2025, https://www.cochranelibrary.com/central/central-creation

13. How Scopus Works: A Comprehensive Guide to Indexing and Abstracting - Manuscriptedit, accessed on January 16, 2025, https://www.manuscriptedit.com/scholar-hangout/how-scopus-works-a-comprehensive-guide-to-indexing-and-abstracting/

14. Where to Search - Systematic Reviews - Research Guides at George Washington University, accessed on January 16, 2025, https://guides.himmelfarb.gwu.edu/systematic_review/medical-literature-databases-to-search

15. Searching for Systematic Reviews & Evidence Synthesis: Searching Databases - KCL LibGuides, accessed on January 16, 2025, https://libguides.kcl.ac.uk/systematicreview/searchdb

16. What is the best scientific database to use for systematic literature review and why?, accessed on January 16, 2025, https://www.researchgate.net/post/What_is_the_best_scientific_database_to_use_for_systematic_literature_review_and_why

17. MEDLINE and MeSH Data Changes — 2023. NLM Technical Bulletin. 2022 Nov–Dec, accessed on January 16, 2025, https://www.nlm.nih.gov/pubs/techbull/nd22/nd22_medline_mesh_data_changes_2023.html

18. May 2023 Update to Emtree(R) Now Available in Embase(R) - STN International, accessed on January 16, 2025, https://www.stn-international.com/en/nachricht/may-2023-update-emtreer-now-available-embaser

19. What's new (search and CENTRAL) - Cochrane Library, accessed on January 16, 2025, https://www.cochranelibrary.com/en/search/releases

20. Scopus AI Release: May 2024 | Elsevier Scopus Blog, accessed on January 16, 2025, https://blog.scopus.com/posts/scopus-ai-release-may-2024

21. Latest Update to Emtree® Now Available in Embase® | STN International, accessed on January 16, 2025, https://www.stn-international.com/en/nachricht/latest-update-emtreer-now-available-embaser

22. Planning the Search - A Research Guide for Systematic Literature Reviews, accessed on January 16, 2025, https://guides.lib.ua.edu/sysreviews/PlanningSearch