REVIEW ARTICLE A systematic review identified few methods and strategies describing when and how to update systematic reviews David Moher a,b,c, * , Alexander Tsertsvadze a , Andrea C. Tricco a,d , Martin Eccles e , Jeremy Grimshaw f , Margaret Sampson a,g , Nick Barrowman a,b a Chalmers Research Group, Children’s Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, Ontario, Canada b Department of Pediatrics, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada c Department of Epidemiology & Community Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada d Institute of Population Health, University of Ottawa, Ottawa, Ontario, Canada e University of Newcastle upon Tyne, Newcastle, UK f Ottawa Health Research Institute, The Ottawa Hospital, Ottawa, Ontario, Canada g Department of Information Studies, University of Wales, Aberystwyth, UK Accepted 14 March 2007 Abstract Objective: Systematic reviews (SRs) are convenient summaries of evidence for health care practitioners. They form a basis for clinical practice guidelines and suggest directions for new research. SRs are most helpful if they are current; however, most of them are not being updated. This SR summarizes strategies and methods describing when and how to update SRs. Study Design and Setting: We searched MEDLINE (1966 to December 2005), PsycINFO, the Cochrane Methodology Register, and the 2005 Cochrane Colloquium proceedings to identify records describing when and how to update SRs in health care. Results: Four updating strategies, one technique, and two statistical methods were identified. Three strategies addressed steps for up- dating, and one strategy presented a model for assessing the need to update. One technique discussed the use of the ‘‘entry date’’ field in bibliographic searching. The statistical methods were cumulative meta-analysis and a test for detecting outdated meta-analyses with statistically nonsignificant results. Conclusion: Little research has been conducted on when and how to update SRs in contrast to other methodological areas of conduct- ing SRs (e.g., publication bias, variance imputation). The feasibility and efficiency of the identified approaches is uncertain. More research is needed to develop pragmatic and efficient methodologies for updating SRs. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Systematic reviews; Updating; Cumulative meta-analysis; Strategy; Methods; Techniques 1. Introduction A systematic review (SR) is a form of convenient syn- thesis of evidence for the busy health care practitioner. SRs are increasingly gaining acceptance as a starting point in the development of evidence-based clinical practice guidelines (CPGs) [1,2], and in the design and ethical guid- ance of primary research [3]. Governments and other groups are investing heavily in commissioning and using the results of SRs to inform health care practice and policy [4]. Recent estimates suggest that approximately 2,500 new SRs are published annually [5]. SRs are most useful if they are up to date [4,6]. As sci- ence evolves with the accumulation of new research and publications, health care interventions previously consid- ered to be effective and safe may in future be shown to be ineffective or harmful, or vice versa [7]. There may also be subtle changes in interventions over time (e.g., changes in dosing of medications, improved surgical skills). As well, new interventions or health outcomes will emerge [8]. Ignoring these changes could undermine the validity of SRs and CPGs. Updating SRs can also be useful in the identification and incorporation of delayed publications or gray literature, allowing to minimize the impact of publica- tion bias (or time lag bias) on results of SRs [9e11]. Organizations such as the Cochrane Collaboration up- date SRs routinely. In contrast, non-Cochrane SRs, which account for about 80% of all published reviews [5], are not usually updated. Within 2 years of their publication, * Corresponding author. Chalmers Research Group, Children’s Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, Ontario, Canada. E-mail address: dmoher@uottawa.ca (D. Moher). 0895-4356/07/$ e see front matter Ó 2007 Elsevier Inc. All rights reserved. doi: 10.1016/j.jclinepi.2007.03.008 Journal of Clinical Epidemiology 60 (2007) 1095e1104