A well-planned and conducted search for studies is a key component of a Cochrane Review.
Cochrane Gut facilitates literature searching for review authors. Usually, the Cochrane information specialist (CIS) will devise a search strategy with authors during the development of a review's protocol. For each review a search strategy is produced based on relevant clinical terms agreed by the author and the CIS.
Review authors should work closely, from the start of the protocol, with an experienced medical/healthcare librarian or information specialist, so they can:
- Consider and contribute to the search strategy
- Understand what the Information Specialist is doing
- Identify any additional searching that can or should be done
- Work with the Information Specialist to report the search strategy accurately in the review
- Studies (not reports of studies) are included in Cochrane Reviews but identifying reports of studies is currently the most convenient approach to identifying the majority of studies and obtaining information about them and their results.
- The Cochrane Central Register of Controlled Trials (CENTRAL) and MEDLINE, together with Embase (if access to Embase is available to the review team) should be searched for all Cochrane Reviews.
- Additionally, for all Cochrane Reviews, the Specialized Register of the relevant Cochrane Review Groups should be searched, either internally within the Review Group or via CENTRAL.
- Trials registers should be searched for all Cochrane Reviews and other sources such as regulatory agencies and clinical study reports (CSRs) are an increasingly important source of information for study results.
- Searches should aim for high sensitivity, which may result in relatively low precision.
- Search strategies should avoid using too many different search concepts but a wide variety of search terms should be combined with OR within each included concept.
- Both free-text and subject headings (e.g. Medical Subject Headings (MeSH) and Emtree) should be used.
- Published, highly sensitive, validated search strategies (filters) to identify randomized trials should be considered, such as the Cochrane Highly Sensitive Search Strategies for identifying randomized trials in MEDLINE (but do not apply these randomized trial or human filters in CENTRAL).
During the development of the review, the CIS executes the search on the following databases,
- The Cochrane Library, which includes The Cochrane Central Register of Controlled Trials (CENTRAL) and the Cochrane Database of Systematic reviews
- Cochrane Specialised Registers
When appropriate, the additional resources are searched, such as:
- National, regional and subject-specific bibliographic databases (e.g. CINAHL for nursing-related topics, PsycINFO for psychological interventions, AMED for alternative therapies; LILACS, etc)
- Ongoing studies and unpublished
- Trials registers and trials results registers
- Regulatory agency sources and clinical study reports
- Other sources
Some conference abstracts and proceedings are indexed in bibliographic databases such as Embase. Embase includes conference abstracts from important biomedical, drug and medical device conferences dating back to 2009. The full list of covered conferences indexed in Embase can be found here.
Occasionally a review team will have sufficient in-house library or information support. In this case the CIS will work with the in-house team, confirming the searches are of a sufficient quality and supplementing the searching where access to particular resources are limited.
CENTRAL is the most comprehensive source available for controlled trials. CENTRAL is comprised of records retrieved from PubMed/MEDLINE, Embase, ClinicalTrials.gov, WHO's ICTRP, KoreaMed, all Cochrane Review Groups' Specialized Registers, and records identified by handsearching various biomedical sources, as described here.
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Lefebvre C, Glanville J, Briscoe S, Littlewood A, Marshall C, Metzendorf M-I, Noel-Storr A, Rader T, Shokraneh F, Thomas J, Wieland LS. Chapter 4: Searching for and selecting studies. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019.
Julian PT Higgins, Toby Lasserson, Jackie Chandler, David Tovey, James Thomas, Ella Flemyng and Rachel Churchill. Methodological Expectations of Cochrane Intervention Reviews (MECIR). Standards for the conduct and reporting of new Cochrane Intervention Reviews, reporting of protocols and the planning, conduct and reporting of updates. Version March 2020.