Cochrane Handbook for Systematic Reviews of Interventions Edited by Julian P. T. Higgins &

s and other grey literature have been shown to be sources of approximately 10% of the studies referenced in Cochrane reviews (Mallett 2002). Over one-half of trials reported in conference abstract never reach full publication, and those that are eventually published in full have been shown to be systematically different than those that are never published in full (Scherer 2003). In addition, grey literature in general has been found to be more likely than health care journals to contain ‘negative’ reports (McAuley 2000). Thus, failure to identify trials reported in conference proceedings might affect the results or threaten the validity of a systematic review. Authors who wish to handsearch journals or conference proceedings to identify reports of studies for their review should first consult with the editorial based of their CRG. The CRG’s Trials Search Coordinator/Review Group Coordinator can determine whether the journal or conference proceedings has already been searched, and, if it has not, the Coordinator can register the search on the Master List and provide training in handsearching. Training material is available on the US Cochrane Center web site (http://www.cochrane.us/hsmain.htm) All correspondence regarding the initiation of a journal search, progress of a journal search, status of a search etc needs to be between staff at the US Cochrane Center and the Trials Search Coordinator/Review Group Coordinator. 5.1.3 Checking reference lists Authors should check the reference lists of articles obtained (including those from previously published systematic reviews) to identify relevant reports. The process of following up references from one article to another is generally an efficient means of identifying studies for possible inclusion in a review. Because investigators may selectively cite studies with positive results (Gotzsche 1987; Ravnskov 1992), reference lists should never be used as a sole approach to identifying reports for a review, but rather as an adjunct to other approaches. 5.1. 4 Checking other reviews Some of the most convenient and obvious sources of references to potentially relevant studies are existing reviews. Copies of previously published reviews on the topic of interest should be obtained and checked for references to the original studies. As well as the Cochrane Database of Systematic Reviews, The Cochrane Library includes the Database of Abstracts of Reviews of Effects (DARE) a database produced by the NHS Centre for Reviews and Dissemination in York, UK, that provides information on previously published reviews of the effects of healthcare. MEDLINE, EMBASE and other bibliographic databases can also be used to identify review articles. In MEDLINE, the most appropriate review articles would be indexed under the Publication Type terms META-ANALYSIS and REVIEW, ACADEMIC. Search strategies have been developed to enhance identification of these types of publication (Boynton 1998). 5.1. 5 Print versions of electronic databases While MEDLINE and EMBASE include citations from 1966 and 1974 to the present, respectively, Index Medicus and Excerpta Medica, the print versions of these databases, include citations from 1879 and 1948, respectively. Searching the earlier printed subject indexes may be worthwhile, especially if there is reason to believe that there were early studies of the intervention being reviewed. Science Citation Index is the print version of SciSearch (see Section 5.1.1.3) and is used for the same general purpose, i.e. for listings of where a published article was subsequently cited. Science Citation Index is more comprehensive than SciSearch, which began in 1974.