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Systematic Reviews: Where to Search

By Paul Levett

Document your search!

You should always document your searches so that you can report your methodology. Many journals will require you to add the full electronic search strategy for each database in an appendix.

In addition to the search strategy, PRISMA checklist Item 7 requires you to report information about your sources including:

  • What databases/websites you searched, the name of the database search platform and the start/end dates the index covers if relevant e.g. OVID MEDLINE (1950-present), or just PubMed
  • Who developed & conducted the searches
  • Date each database/website was last searched
  • Supplementary sources - what other websites did you search? What journal titles were hand searched, whether reference lists were checked, what trial registries or regulatory agency websites were searched, were manufacturers or other authors contacted to obtain unpublished or missing information on study methods or results.

Top 3 Databases

At a minimum you should search MEDLINE, EMBASE, and the Cochrane CENTRAL trials register. This is the recommendation of three medical and public health research organizations: the U.S. Agency for Healthcare Research and Quality (AHRQ), the U.K. Centre for Reviews and Dissemination (CRD), and the International Cochrane Collaboration (Source: Institute of Medicine (2011) Finding What Works in Healthcare: Standards for Systematic Reviews Table E-1, page 267).  Some databases have an alternate version that search the same records: the content of MEDLINE is in PubMed, while the content of EMBASE is in Scopus. You should reformat your search for each database as appropriate, contact your librarian if you want help on how to search each database.  

Begin by searching:

1.       MEDLINE (or PubMed)

AND

2.       EMBASE (or Scopus)  Please note Himmelfarb Library does not have a subscription to EMBASE. The content is in the Scopus database that you can search using keywords, but it is not possible to perform an EMTREE theasaurus search in Scopus.

AND

3.       Cochrane Central Trials Register (or Cochrane Library). In addition Cochrane researchers recommend you search the clinicaltrials.gov and ICTRP clinical trial registries.

Search Tools

The Polyglot Search Translator is a very useful tool for translating search strings from PubMed or Medline via Ovid across multiple databases, developed by the Institute for Evidence-Based Healthcare at Bond University. But please note Polyglot does not automatically map subject terms across databases (e.g. MeSH terms to Emtree terms) so you will need to manually edit the search syntax in a text editor to change to the actual subject terms used by another database.

The Yale Mesh Analyzer is another very useful tool you can copy and paste in a list of up to 20 PMID numbers for records in the PubMed database, the Yale Mesh Analyzer will then display the Mesh Medical Subject Headings for those 20 articles as a table so you can identify and compare what Mesh headings they have in common, this can suggest additional search terms for your PubMed search.

The MedSyntax tool is another useful tool, for parsing out very long searches with many levels of brackets. This would be useful if you are trying to edit a pre-existing search strategy with many levels of parentheses.

Finding Pre-Existing Search Filters

Some sources for pre-existing database search filters or "hedges" include:

Supplementary resources to search

Other members of your investigative team may have ideas about databases, websites, and journals they think you should search. Searching these sources is not required to perform a systematic review. You may need to reformat your search keywords.

Researchers at GW should check our subject research guides for suggestions, or check the libguides community for a guide on your subject.

In addition you may wish to search one or more of the following resources:

  • Google Scholar
  • BASE academic search engine is useful for searching in University Institutional Repositories
  • Cochrane Database of Systematic Reviews to search for a pre-existing systematic review on your topic
  • Epistemonikos database, has a matrix of evidence table so you can see what citations are shared in common across existing systematic reviews of the same topic. This feature might help identify sentinel or 'don't miss' articles.

You might also consider searching one or more of the following websites depending on your topic:

Clinical trial registers. The Cochrane Collaboration recommends for a systematic review to search both clinicaltrials.gov and the WHO ICTRP (See http://handbook.cochrane.org/ section 4.3):

Guidelines

Grey literature resources:

Preprints 

  • See our Himmelfarb preprints guide page on finding preprints, a useful database for searching Health Sciences preprints is Europe PMC

Dissertations and Theses:

Conference proceedings:

  • BASE academic search engine, has an Advanced Search feature with a Limit by Type to 'Conference Objects', this is useful for searching for conference posters and submissions stored in University Institutional Repositories.
  • Web of Science - click All Databases and select Core Collection - under More Settings limit to the Conference Proceedings Citation Index (CPCI) - searches a limited set of conferences on Science, Social Science and Humanities from 1990-present.
  • Scopus - Limit Document Type to Conference Paper or Conference Review.
  • Proquest - Limit search results to conference papers &/or proceedings under Advanced Search.
  • BioMed Central Proceedings - searches a limited set of biomedical conference proceedings, including bioinformatics, genetics, medical students, and data visualization.
  • F1000 Research - browse by subject and click the tabs for articles, posters, and slides - which searches a limited number of biology and medical society meetings/conferences. This is a voluntary self-archive repository.

Individual Journals 

  • You may choose to "hand search" select journals where the research team reads the Table of Contents of each issue for a chosen period of time.  You can look for the names of high impact journal titles in a particular field indexed in Journal Citation Reports (JCR).