Electronic bibliographical databases and their limitations


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In the age of evidence-based medicine, being able to search for relevant research to answer a question is crucial to both scientists and clinicians. At the same time, computers and the internet have revolutionised medical publishing. With thousands of research articles being published each year, bibliographic databases provide a way to search the archives of multiple journals from across the world.

A bibliographic database is a repository of bibliographic or publication records. It provides an index of journal articles from multiple journals, and includes citations, abstracts and often a link to the full text. Databases are available online, so they can be updated regularly and easily accessed.

The Medline database

Medline is perhaps the best known bibliographic database, and can be accessed free of charge via several online portals including PubMed. It is compiled by the National Library of Medicine of the United States and in 1997 was thought to have included around 30-40% of the 10 million biomedical articles that had been published.1 Encompassing articles published since 1946, Medline currently indexes citations from approximately 5,600 biomedical journals in 40 languages. 806,000 citations were added in 2015 alone.2

Articles can be traced in two ways: by terms including words in the title, abstract, authors' names, or institution, or by a restricted thesaurus of hierarchically grouped medical terms, known as Medical Subject Headings (MeSH terms).1 As with other databases, multiple search terms can be used simultaneously by combining them with the Boolean operators AND, OR and NOT.

The best way to learn about bibliographic databases is to use them. Trisha Greenhalgh’s article1 includes several worked examples that can be replicated in Medline.


Embase, published by Elsevier, is another biomedical database consisting of around 30 million records from 8500 journals, with records dating back to 1974 (although Embase Classic includes citations dating back to 1947).3 There is an overlap in coverage between Embase and Medline, but the former includes over 6 million citations that are not in Medline. Embase is more comprehensive on pharmacological literature and alternative therapies.

Other databases

Other frequently used biomedical databases include:

  • CINAHL (Cumulative Index of Nursing and Allied Health Literature) – indexes nursing and allied health journals
  • Cochrane Library – includes Cochrane reviews, and Cochrane’s central register of controlled trials (CENTRAL), as well as health technology assessments and economic evaluations.
  • Google Scholar – as well as journals and conferences papers, this includes books, dissertations, technical reports and patents
  • PsychINFO – indexes psychological, social and behavioural science articles from the 1880s onwards
  • Scopus – includes peer-reviewed journals in the scientific, technical, medical and social sciences
  • Web of Science – includes coverage of the sciences, social sciences, arts and humanities

Limitations of electronic databases

  • Databases may not contain the most recent references
  • Search results from bibliographic databases depend on the search strategy used and the quality of the indexing.
  • Obtaining a comprehensive selection of references can involve searching several databases because their coverage varies and no single database accesses all available literature
  • Most databases only include published articles; it is necessary to search separately for grey literature
  • There is often a bias towards citations written in English



  1. Greenhalgh, T. How to read a paper: The Medline database. BMJ 1997 315: 180-183
  2. http://www.nlm.nih.gov/pubs/factsheets/medline.html - Accessed 8/04/17
  3. https://www.elsevier.com/solutions/embase-biomedical-research/embase-coverage-and-content– Accessed 8/04/17


© Helen Barratt 2009, Saran Shantikumar 2018