Comparison of descriptions of allocation concealment in trial protocols and the published reports: cohort study
Open accessAbstract
OBJECTIVES: To compare how allocation concealment is described in publications of randomised clinical trials and corresponding protocols, and to estimate how often trial publications with unclear allocation concealment have adequate concealment according to the protocol. DESIGN: Cohort study of 102 sets of trial protocols and corresponding publications. SETTING: Protocols of randomised trials approved by the scientific and ethical committees for Copenhagen and Frederiksberg, 1994 and 1995. MAIN OUTCOME MEASURES: Frequency of adequate, unclear, and inadequate allocation concealment and sequence generation in trial publications compared with protocols, and the proportion of protocols where methods were reported to be adequate but descriptions were unclear in the trial publications. RESULTS: 96 of the 102 trials had unclear allocation concealment according to the trial publication. According to the protocols, 15 of these 96 trials had adequate allocation concealment (16%, 95% confidence interval 9% to 24%), 80 had unclear concealment (83%, 74% to 90%), and one had inadequate concealment. When retrospectively defined loose criteria for concealment were applied, 83 of the 102 trial publications had unclear concealment. According to their protocol, 33 of these 83 trials had adequate allocation concealment (40%, 29% to 51%), 49 had unclear concealment (59%, 48% to 70%), and one had inadequate concealment. CONCLUSIONS: Most randomised clinical trials have unclear allocation concealment on the basis of the trial publication alone. Most of these trials also have unclear allocation concealment according to their protocol.
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The method of sequence generation was not described in three quarters of randomised trial protocols approved by a research ethics committee in Denmark in 1994-95, and a US cooperative cancer research group in 1968-2006.
“The method of sequence generation was not described in three quarters of randomised trial protocols approved by a research ethics committee in Denmark in 1994-95, and a US cooperative cancer research group in 1968-2006.329 330”
From SPIRIT 2025 explanation and elaboration: updated guideline for protocols of randomised trials (2025) · cites this paper as [329]
In one study of randomised trial protocols in Denmark, more than half did not adequately describe allocation concealment methods.
“In one study of randomised trial protocols in Denmark, more than half did not adequately describe allocation concealment methods.329”
From SPIRIT 2025 explanation and elaboration: updated guideline for protocols of randomised trials (2025) · cites this paper as [329]
Similar results on outcome reporting bias have been reported in other jurisdictions.
“These disturbing results have been reported in other jurisdictions. 12,13”
From Reporting research results: a moral obligation for all researchers. (2007) · cites this paper as [13]
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- Nordic Cochrane Centre, H:S Rigshospitalet, DK-2100 Copenhagen, Denmark Julie Pildal research fellow Asbjørn Hróbjartsson senior research fellow Elisabeth Forfang physician Peter C Gøtzsche director Department of Medicine, University of Toronto An-Wen Chan resident physician Cancer Research UK Medical Statistics Group, Centre for Statistics in Medicine, Oxford OX3 7LF
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Self-citation
- Authors
- Pildal, J., Chan, A.-W., Hróbjartsson, A., Forfang, E., Altman, D. G., & Gøtzsche, P. C.
- Affiliations
- Rigshospitalet (DK)
- University of Toronto (CA)
- Cancer Research UK (GB)
- Corresponding author
- Pildal, Julie
- Venue
- BMJ
- Publisher
- BMJ
- Published
- 2005-04-07
- Volume
- 330
- Issue
- 7499
- Pages
- 1049
- ISSN
- 0007-1447 (ISSN-L)
- 0959-8138
- 1468-5833
- PMC
- PMC557221
- OpenAlex
- W2144441836
- Cited by
- 209
- References
- 26
- Citations by year
- 2026: 3 · 2025: 5 · 2024: 11 · 2023: 5 · 2022: 6 · 2021: 7 · 2020: 7 · 2019: 5 · 2018: 10 · 2017: 7 · 2016: 13 · 2015: 10 · 2014: 5 · 2013: 14 · 2012: 14
- FWCI
- 19.09
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- BMJ (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- HighWire Press Open Archive (submittedVersion)
- DigitalGeorgetown (Georgetown University Library) (submittedVersion)
- Funders
- Cancer Research UK
- Topics
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmaceutical industry and healthcare
- Keywords
- allocation concealment, randomized controlled trials, sequence generation
- MeSH terms
- Random Allocation, Cohort Studies, Randomized Controlled Trials as Topic
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