Searches for studies

For any questions or assistance with development of search strategies and searches of electronic databases, please contact The CHBG Information Specialist, Sarah Louise Klingenberg.


According to the Methodological Expectations of Cochrane Intervention Reviews (MECIR), it is mandatory to plan the methods for identification of studies at the protocol level. Review authors together with the Information Specialist of The CHBG, will develop preliminary search strategies that are expected to meet the eligibility criteria for the review and ensure that relevant time periods and sources are covered. Preferably, searches shall not be restricted by language or publication status.

In the "Search methods for identification of studies" part of the Cochrane protocol, review authors are expected to describe in detail all the electronic database sources planned to be searched as well as the expected time span of search for each one of them. The following text can be used:

“We will search the Cochrane Hepato-Biliary Group Controlled Trials Register (maintained and searched internally by the CHBG Information Specialist via the Cochrane Register of Studies Web), the Cochrane Central Register of Controlled Trials (CENTRAL; latest issue) in the Cochrane Library, MEDLINE Ovid (1946 to the date of the search), Embase Ovid (1974 to the date of the search), LILACS (Bireme; 1982 to the date of the search), Science Citation Index Expanded (Web of Science, 1900 to the date of the search), and Conference Proceedings Citation Index-Science (Web of Science; to the date of the search) (Royle 2003). Appendix XX gives the search strategies with the time spans of the searches.”

The preliminary search strategies shall be provided in an Appendix as a table with three columns. The table should show the Database source, the Date of search (Time span), and the Search strategies developed for each of the respective databases, and with one row per database.

Any other resources planned to be searched must also be specified in the text, e.g.

“Furthermore, we will search the Food and Drug Administration (FDA) (, European Medicines Agency (EMA) (, WHO International Clinical Trial Registry Platform (, (, as well as pharmaceutical company sources, reference lists of potentially eligible studies, and relevant reviews for ongoing or unpublished trials. We will also search for grey literature in the System for Information on Grey Literature in Europe “OpenGrey” (”

Links to the URL should be provided for each of the web-based resources.


Royle 2003 
Royle P, Milne R. Literature searching for randomized controlled trials used in Cochrane reviews: rapid versus exhaustive searches. International Journal of Technology Assessment in Health Care 2003;19(4):591-603.


At the review level, the Group’s Information Specialist will also assist in performing electronic searches in database sources where access is available. The electronic searches will be executed as described in the protocol unless any updates or adjustments are needed. All identified and downloaded records will be managed in the Cochrane Register of Studies Web software. Search results will be sent to the review authors through the tracking feature of the system. This feature keeps track of all records sent to a specific review and ensures that authors do not receive the same records twice. Authors will receive the results of the searches by e-mail, in text format that is directly compatible with both Review Manager and Covidence (  (see 'Study selection' below).

The search process shall be documented in sufficient detail in the review so that all the searches of all the databases can be reproduced. At review level, the description of the search process in the text shall be changed to past tense or as sensible, and the date of search must be reported at all relevant places in the review text. The search strategies shall be provided in an Appendix (preferably copy-pasted to avoid typos and spelling mistakes). The number of hits for each line or each database are not needed in the Appendix.

Update of searches

According to the MECIR Guidelines, the searches must be rerun close to publication if the initial search date is more than 12 months (preferably six months) from the intended publication date, and the results screened for potentially eligible studies. Ideally the studies should be incorporated fully in the review. If not, then the potentially eligible studies will need to be reported, minimum as references, in ‘Studies awaiting classification’ (or ‘Ongoing studies’ if they have not yet been completed).

In addition, searches will be rerun when a review needs to be updated (See Handbook Chapter IV, section 2, for further information on whether or when to update a Cochrane Review).

Study selection

During the selection of studies it is important to be aware of multiple records for the same study, including abstracts or trial protocols from trial registers or both, no matter whether these include any data or not, or publications not directly reporting on a randomised clinical trial but are related to the study by reporting on specific outcomes, e.g. adverse events.

Decisions should be documented for all records identified by the search. Details of the flow of studies from the number(s) of references identified in the searches to the number of studies included in the review will need to be reported in the final review, ideally using a PRISMA flow diagram which can be generated directly in Review Manager. For the update of reviews including new search results in addition to already included studies, an adapted version of the PRISMA flow diagram is recommended.

An Excel spread sheet, designed to help authors keep track of their references in order to populate the PRISMA study flow diagram in their review, is here.

Covidence is the primary screening and data extraction tool for Cochrane authors conducting standard intervention reviews. Covidence is designed to make review production more efficient and is tailored to Cochrane methods. Covidence allows the author team to:

• upload search results 
• screen abstracts and full text study reports 
• complete data collection 
• conduct risk of bias assessment 
• resolve disagreements
• export data into RevMan or Excel

Please find more information about Covidence on Cochrane Community and references

Please make sure to follow the Cochrane Style Manual for entering references.