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Retrieval barriers in individual participant data reviews with network meta-analysis
  1. Areti Angeliki Veroniki1,2,
  2. Lesley A Stewart3,
  3. Susan P C Le1,
  4. Mike Clarke4,
  5. Andrea C Tricco1,5,
  6. Sharon E Straus1,6
  1. 1 Knowledge Translation Program, St Michael's Hospital, Unity Health Toronto, Toronto, Ontario, Canada
  2. 2 Institute of Health Policy Management and Evaluation, University of Toronto, Toronto, Ontario, Canada
  3. 3 Centre for Reviews and Dissemination, University of York, York, UK
  4. 4 Queen’s University Belfast, Belfast, UK
  5. 5 Epidemiology Division & Institute of Health Policy, Management, and Evaluation, Dalla Lana School of Public Health University of Toronto, Toronto, Ontario, Canada
  6. 6 Department of Geriatric Medicine, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Dr Areti Angeliki Veroniki, Knowledge Translation Program, St Michael's Hospital, Unity Health Toronto, Toronto, ON M5B 1T8, Canada; areti-angeliki.veroniki{at}


Objectives Individual participant data (IPD) from randomised controlled trials (RCTs) can be used in network meta-analysis (NMA) to underpin patient care and are the best analyses to support the development of guidelines about the use of healthcare interventions for a specific condition. However, barriers to IPD retrieval pose a major threat. The aim of this study was to present barriers we encountered during retrieval of IPD from RCTs in two published systematic reviews with IPD-NMA.

Methods We evaluated retrieval of IPD from RCTs for IPD-NMA in Alzheimer’s dementia and type 1 diabetes. We requested IPD from authors, industry sponsors and data repositories, and recorded IPD retrieval, reasons for IPD unavailability, and retrieval challenges.

Results In total, we identified 108 RCTs: 78 industry sponsored, 11 publicly sponsored and 19 with no funding information. After failing to obtain IPD from any trial authors, we requested it from industry sponsors. Seven of the 17 industry sponsors shared IPD for 12 950 participants (59%) through proprietary-specific data sharing platforms from 26 RCTs (33%). We found that lack of RCT identifiers (eg, National Clinical Trial number) and unclear data ownership were major challenges in IPD retrieval. Incomplete information in retrieved datasets was another important problem that led to exclusion of RCTs from the NMA. There were also practical challenges in obtaining IPD from or analysing it within platforms, and additional costs were incurred in accessing IPD this way.

Conclusions We found no clear evidence of retrieval bias (where IPD availability was linked to trial findings) in either IPD-NMA, but because retrieval bias could impact NMA findings, subsequent decision-making and guideline development, this should be considered when assessing risk of bias in IPD syntheses.

  • methods
  • systematic reviews as topic

Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

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Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

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  • Contributors AAV, ACT and SES conceived and designed the study. AAV abstracted data, contacted sponsors, analysed data, interpreted results, and wrote a draft manuscript. AAV is the guarantor of the study. SPCL contacted authors, sponsors and data sharing repositories, and edited the manuscript. LAS, MC, ACT, and SES provided input into the design, interpreted results, and edited the manuscript. All authors read and approved the final manuscript.

  • Funding SES is funded by a Tier 1 Canada Research Chair in Knowledge Translation. ACT is funded by a Tier 2 Canada Research Chair in Knowledge Synthesis.

  • Competing interests AAV is on the editorial board for the journal but was not involved with the peer review process or decision to publish.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.