Intended for healthcare professionals

CCBYNC Open access

Impact of CONSORT extension for cluster randomised trials on quality of reporting and study methodology: review of random sample of 300 trials, 2000-8

BMJ 2011; 343 doi: (Published 26 September 2011) Cite this as: BMJ 2011;343:d5886
  1. N M Ivers, family physician1,
  2. M Taljaard, scientist2,
  3. S Dixon, postdoctoral fellow3,
  4. C Bennett, research coordinator2,
  5. A McRae, research director4,
  6. J Taleban, PhD candidate5,
  7. Z Skea, research fellow6,
  8. J C Brehaut, scientist2,
  9. R F Boruch, professor of education and statistics7,
  10. M P Eccles, professor of clinical effectiveness8,
  11. J M Grimshaw, senior scientist2,
  12. C Weijer, professor of philosophy and medicine9,
  13. M Zwarenstein, senior scientist10,
  14. A Donner, professor of epidemiology and biostatistics11
  1. 1Women’s College Hospital, 76 Grenville Street, Toronto, ON, Canada M5S 1B2
  2. 2Ottawa Hospital Research Institute, Clinical Epidemiology Program, Ottawa Hospital, Civic Campus, 1053 Carling Avenue, Ottawa, ON
  3. 3Department of Epidemiology and Biostatistics, Schulich School of Medicine and Density, University of Western Ontario, London, ON
  4. 4Division of Emergency Medicine, University of Calgary, Foothills Medical Centre, 1403-29 Street NW, Calgary, AB
  5. 5Department of Epidemiology and Biostatistics, University of Western Ontario, London, ON
  6. 6Health Services Research Unit, Health Sciences Building, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK
  7. 7Graduate School of Education, University of Pennsylvania, 3700 Walnut Street, Philadelphia, PA 19104, USA
  8. 8Institute of Health and Society, Newcastle University, Baddiley-Clark Building, Newcastle upon Tyne
  9. 9Rotman Institute of Philosophy, Department of Philosophy, University of Western Ontario, London, ON
  10. 10Institute for Clinical Evaluative Sciences and Sunnybrook Research Institute, G106 - 2075 Bayview Avenue, Toronto, ON
  11. 11Schulich School of Medicine and Dentistry, Kresge Building, University of Western Ontario, London, ON
  1. Correspondence to: N M Ivers noah.ivers{at}
  • Accepted 9 August 2011


Objective To assess the impact of the 2004 extension of the CONSORT guidelines on the reporting and methodological quality of cluster randomised trials.

Design Methodological review of 300 randomly sampled cluster randomised trials. Two reviewers independently abstracted 14 criteria related to quality of reporting and four methodological criteria specific to cluster randomised trials. We compared manuscripts published before CONSORT (2000-4) with those published after CONSORT (2005-8). We also investigated differences by journal impact factor, type of journal, and trial setting.

Data sources A validated Medline search strategy.

Eligibility criteria for selecting studies Cluster randomised trials published in English language journals, 2000-8.

Results There were significant improvements in five of 14 reporting criteria: identification as cluster randomised; justification for cluster randomisation; reporting whether outcome assessments were blind; reporting the number of clusters randomised; and reporting the number of clusters lost to follow-up. No significant improvements were found in adherence to methodological criteria. Trials conducted in clinical rather than non-clinical settings and studies published in medical journals with higher impact factor or general medical journals were more likely to adhere to recommended reporting and methodological criteria overall, but there was no evidence that improvements after publication of the CONSORT extension for cluster trials were more likely in trials conducted in clinical settings nor in trials published in either general medical journals or in higher impact factor journals.

Conclusion The quality of reporting of cluster randomised trials improved in only a few aspects since the publication of the extension of CONSORT for cluster randomised trials, and no improvements at all were observed in essential methodological features. Overall, the adherence to reporting and methodological guidelines for cluster randomised trials remains suboptimal, and further efforts are needed to improve both reporting and methodology.


  • We thank the editors as well as the reviewers, Sandra Eldridge and Carol Coupland, for their insightful comments, which have led to substantial improvements on an earlier version of this manuscript.

  • Contributors: NMI, MT, CW, JMG, JCB, MPE, AD, ZS, and RFB contributed to the conception and design of the study. NMI drafted the article and is guarantor. MT conducted the analysis of the data. All authors contributed to the interpretation of the data, commented on the first draft, revised the article critically for important intellectual content, and approved the final version. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis.

  • Funding: This study was funded by operating grants MOP85066 and MOP89790 from the Canadian Institutes of Health Research. The funding agency had no role in the study design, collection, analysis or interpretation of data, writing of the manuscript or in the decision to submit the manuscript for publication. NMI and AMcR both hold a fellowship award from the Canadian Institutes of Health Research. JMG and CW both hold Canada Research Chairs.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: Not required.

  • Data sharing: Technical appendix, statistical code, and dataset are available from the corresponding author.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: and

View Full Text