REGISTER OF ONGOING SYSTEMATIC REVIEWS
International register of ongoing systematic reviews
Background
Support for prospective registration of systematic review protocols has been gathering momentum, reflected in a number of recently published papers.1-4 The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions advocates registration and the PRISMA 2009 Checklist requires protocol registration details, if available, to include a registration number and details of the existence of and access to the protocol.1, 2 Following publication of the 2009 PRISMA statement, CRD received a number of unsolicited applications for registration of review protocols, an indication that the systematic review community is ready to support such a register.
Well conducted systematic reviews are accepted as best quality evidence for policy and practice, and the number of systematic reviews published has risen dramatically.5 Given the widening range of settings where reviews are being undertaken, and the increasing requirement for systematic reviews as a compulsory precursor to primary research, this trend is set to continue.3, 6
Many of the developments in systematic review and meta-analysis methodology have focussed on minimising the risk of bias within reviews.7-9 There is now concern about, and evidence of publication bias and of selective outcome reporting associated with systematic reviews.10-15 An open register of reviews at the protocol stage would provide an unbiased listing of systematic reviews being produced. This would offer transparency and encourage publication or at least provide knowledge of existence of a review. In either case the facility would assist in assessing and therefore reducing the risk of publication bias. In addition a register would enable discrepancies between published analyses and those planned in the registered review protocol12 to be more readily identified, thereby discouraging bias when reporting outcomes.
There is evidence that Cochrane reviews are more likely to report the use of a protocol than non-Cochrane published reviews. This is likely to be because Cochrane protocols are published a priori, and the difference in wording constraints between publication in the Cochrane Library and journal articles.13 Citing protocol registration details in accordance with the PRISMA checklist, would be a succinct way of confirming a systematic approach to the review within the confines of publication word limits.
A register of review protocols could assist in planning new reviews and updating of existing ones. This would also help in optimising the use of research funds by enabling funding and commissioning agencies to avoid unnecessary duplication and encourage collaboration. A comprehensive register could also create opportunities for methodological and other research, both within and across disciplines.
Existing registers are limited to the outputs of their organisations. Prospective authors of Cochrane reviews are required to register a title with the relevant Cochrane review group, the editors of the review group then invite the authors to prepare a protocol. Once approved, Cochrane review protocols are entered into the Cochrane Database of Systematic Reviews (CDSR). The Campbell Collaboration and the Joanna Briggs Institute both publish details of the protocols of systematic reviews being undertaken by their members and the National Public Health Service for Wales is piloting an all Wales systematic review register. Until now there has been no international, centralised, comprehensive register of ongoing reviews; existing registration of protocols being limited to individual organisations such as the Cochrane and Campbell Collaborations. With 80% of systematic reviews generated outside of these collaborations, an international register has the potential for major impact.
References
1. Liberati A, Altman DG, Tetzlaff J, Mulrow C, the PRISMA Group. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. PLoS Med 2009;6: e1000100
2. Moher D LA, Tetzlaff J, Altman DG, for the PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med 2009;339:b2535
3. Straus S, Moher D. Registering systematic reviews. CMAJ 2009;0: cmaj.081849. Available from: www.cmaj.ca/cgi/rapidpdf/cmaj.081849v1
4. Jüni P, Egger M. PRISMAtic reporting of systematic reviews and meta-analyses. The Lancet 2009;374:1221-23.
5. Booth A, Clarke M, Ghersi D, Moher D, Petticrew M, Stewart L. An international registry of systematic-review protocols. Lancet 2010. Published Online July 13, 2010 DOI: 10.1016/S0140-6736(10)60903-8.
6. Clarke M, Hopewell S, Chalmers I. Clinical trials should begin and end with systematic reviews of relevant evidence: 12 years and waiting. Lancet 2010. 376(9734 ): 20-21
7. Song F, Eastwood AJ, Gilbody S, Duley L, Sutton AJ. Publication and related biases. Health Technol Assess 2000;4:1-115.
8. Higgins JPT, Green S, (editors). Cochrane Handbook for Systematic Reviews of Interventions. Version 5.0.0 [updated February 2008]: The Cochrane Collaboration; 2008. Available from: www.cochrane-handbook.org
9. Centre for Reviews and Dissemination. Core principles and methods for conducting a systematic review of health interventions. In: Systematic reviews: CRD's guidance for undertaking reviews in health care. York: University of York; 2009. p. 2-99.
10. Kirkham JJ, Altman DG, Williamson PR. Bias due to changes in specified outcomes during the systematic review process. PLoS ONE 2010;5: e9810.PubMed
11. Kirkham JJ, Dwan KM, Altman DG, et al. The impact of outcome reporting bias in randomised controlled trials on a cohort of systematic reviews. BMJ 2010;15; 340: c365. doi: 10.1136/bmj.c365
12. Silagy CA, Middleton P, Hopewell S. Publishing protocols of systematic reviews: comparing what was done to what was planned. JAMA 2002;287:2831-4.
13. Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG. Epidemiology and reporting characteristics of systematic reviews. PLoS Med 2007;4:e78.
14. PLoS Medicine Editors. Many reviews are systematic but some are more transparent and completely reported than others. PLoS Med 2007;4:e147.
15. Dwan K, Altman DG, Arnaiz JA, Bloom J, Chan A-W, Cronin E, et al. Systematic Review of the Empirical Evidence of Study Publication Bias and Outcome Reporting Bias. PLoS ONE 2008;3:e3081.