Searches for systematic reviews should be as extensive as possible, and should cover multiple databases, grey literature and other sources.
The literature search for a systematic review should:
Choosing databases to search
You will need to search multiple databases for a comprehensive search. At least two, but generally no more than five, is recommended.
Databases should be selected with consideration of the topics covered and types of material indexed. When choosing each database, you might consider:
For systematic reviews in health topics, it is recommended to search MEDLINE (via Ovid or PubMed). If the type of evidence required to answer the question includes RCTs, then CENTRAL should also be searched.
Additional subject-specific and region-specific databases should be selected based on review topic or context.
For example, for a nursing-related review additional databases could include CINAHL, Emcare, and/or Health Collection (Informit).
A multidisciplinary database such as Web of Science could be searched as well; this database indexes a diverse range of topics and increases search sensitivity.
Types of databases:
Database vs platform
It is important to know the difference between a database and a platform if you are undertaking a systematic review.
Databases are organised, indexed collections of records with descriptive information, which facilitate searching. Bibliographic references contained in a bibliographic database can include articles, books, conference proceedings, etc. Databases vary in scope, subject focus, publishers and journals indexed. A well-documented database search that is reproducible and transparent is a fundamental component of a systematic review search. CINAHL, PsycINFO and Web of Science are examples of databases.
Platforms are search interfaces that provide access to databases. Some platforms host multiple databases and allow searching of individual or multiple databases. However, for a systematic review you should always search databases individually. Some databases can be accessed through multiple platforms; for example, the database MEDLINE can be searched through the platforms Ovid, Web of Science, and PubMed. Coverage may differ depending on the platform used to access the database.
When reporting your search in your systematic review, you should name each individual database searched and the platform used (PRISMA-S).
Indexes journals, reviews, conferences, patents and books in the life and biomedical sciences.
The most comprehensive database for veterinary and animal science and agriculture.
Covers nursing and allied health topics including audiology, nutrition and dietetics, occupational therapy, physical therapy, respiratory therapy, speech-language therapy, counselling, mental health and consumer health. CINAHL User Guide
This database provides broad coverage of clinical and biomedical literature, and provides access to over 900 full text biomedicine journals.
A full text and indexing database of over 100 Australian and New Zealand health sciences resources.
The link will take you to the main Informit platform - select the database, Health Collection.
The United States National Library of Medicine's premier bibliographic database for medicine, nursing, veterinary medicine, allied health, and the pre-clinical sciences.
The United States National Library of Medicine's premier bibliographic database for medicine, nursing, veterinary medicine, allied health, and the pre-clinical sciences. MEDLINE User Guide
Multidisciplinary collection of journals, magazines and theses, which includes many business, management and economics resources.
Indexes and abstracts over 1300 journals in more than 25 languages. Includes book chapters, books, technical reports and citations to dissertations. Covers professional and academic literature in the field of psychology and psychological aspects of related disciplines.
Includes over 18 million citations from MEDLINE and other life science journals. Subject coverage includes all areas of medicine and related disciplines. Links to full text journals are also available in PubMed Central as well as links to a series of molecular and genome databases.
A multidisciplinary database which is very strong in the sciences and has many useful search features. It includes all of the journals indexed in MEDLINE.
Provides access to all of the Web of Science citation indexes: Science Citation Index Expanded, Social Sciences Citation Index and Arts & Humanities Citation Index.
Browse by subject or category.
The Campbell Collaboration is an international research network that produces systematic reviews of the effects of social interventions in Crime & Justice, Education, International Development and Social Welfare
The Database of Abstracts of Reviews of Effects (DARE) and the NHS Economic Evaluation Database (NHS EED) provide access to:
Indexes journals, reviews, conferences, patents and books in the biological and biomedical sciences
Provides resources for evidence-based research including best practice information sheets, systematic reviews and electronic journals and conference papers. Consumer health-care information is also available
Includes systematic reviews and reviews of clinical trials
The term grey literature "is usually understood to mean literature that is not formally published in sources such as books or journal articles" (Lefebvre, Manheimer, & Glanville, 2008, p. 106).
Grey literature may include multiple types of document produced on all levels of government and by academics, businesses and organisations in electronic and print formats where publishing is not the primary activity of the producing body. (Greynet, 2015.)
There may also be grey literature that is specifically relevant to your discipline.
Practice guidelines are highly relevant to nursing and health professions, working papers are used in the social sciences (particularly economics) and patents are important to engineering.
A systematic review conducted in 2008 by members of the Cochrane methodologies team found that the results from grey literature often have a significant effect on the outcome of a review, as they often report more negative or inconclusive data than published journal articles (Hopewell et al., 2008).
As such, it is important to treat grey literature as another potential source of studies for inclusion while noting that it is usually not subject to peer review and must be evaluated accordingly.
1. Alberani, V., De Castro Pietrangeli, P. & Mazza, A.M. (1990). The use of grey literature in health sciences: A preliminary survey. Bulletin of the Medical Library Association, 78 (4) : 358-363. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC225438/
2. GreyNet International (2015). Retrieved from http://www.greynet.org
3. Lefebvre C, Manheimer E, Glanville J. (2008). Searching for studies. In: J.P.T. Higgins & S. Green (Eds.), Cochrane handbook for systematic reviews of interventions. Chichester: Wiley-Blackwell.
4. Hopewell S, McDonald S, Clarke M, & Egger M. (2007).
Grey literature in meta-analyses of randomized trials of health care interventions. The Cochrane Library. doi: 10.1002/14651858.MR000010.pub3
Government departments (State and Commonwealth) can be found using Google. Some useful sites are listed below:
University repositories, such as the Murdoch Research Portal, can be used to locate theses, research papers and data if they have been made available.
Information about locating theses and dissertations can be found in the Murdoch Library Theses Guide.
Use the Document Type/Source Type/ Publication Type filters to search for specific formats of grey literature.
Guidelines & Standards
In addition to the sources listed above, internet searching can locate other useful sources:
When developing a search strategy, specify what type of content is to appear in search results.
Example search words to include:
thesis OR dissertation OR doctorate
government AND (report OR strategy)
"working paper" OR "white paper" OR "green paper"
(conference OR seminar OR symposium OR workshop) AND (paper OR proceedings)
Internet searches can include file types:
You should evaluate grey literature in the same way as other document types that are included in your research.
The AACODS checklist created by Flinders University is also a useful tool for evaluation and critical appraisal of grey literature.