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What is meant by intention to treat analysis? Survey of published randomised controlled trials
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Abstract Objectives: To assess the methodological quality of intention to treat analysis as reported in randomised controlled trials in four large medical journals. Design: Survey of all reports of randomised controlled trials published in 1997 in the BMJ, Lancet, JAMA, and New England Journal of Medicine. Main outcome measures: Methods of dealing with deviations from random allocation and missing data. Results: 119 (48%) of the reports mentioned intention to treat analysis. Of these, 12 excluded any patients who did not start the allocated intervention and three did not analyse all randomised subjects as allocated. Five reports explicitly stated that there were no deviations from random allocation. The remaining 99 reports seemed to analyse according to random allocation, but only 34 of these explicitly stated this. 89 (75%) trials had some missing data on the primary outcome variable. The methods used to deal with this were generally inadequate, potentially leading to a biased treatment effect. 29 (24%) trials had more than 10% of responses missing for the primary outcome, the methodsof handling the missing responses were similar in this subset. Conclusions: The intention to treat approach is often inadequately described and inadequately applied. Authors should explicitly describe the handling of deviations from randomised allocation and missing responses and discuss the potential effect of any missing response. Readers should critically assess the validity of reported intention to treat analyses. Key messages Intention to treat gives a pragmatic estimate of the benefit of a change in treatment policy rather than of potential benefit in patients who receive treatment exactly as planned Full application of intention to treat is possible only when complete outcome data are available for all randomised subjects About half of all published reports of randomised controlled trials stated that intention to treat was used, but handling of deviations from randomised allocation varied widely Many trials had some missing data on the primary outcome variable, and methods used to deal with this were generally inadequate, potentially leading to bias Intention to treat analyses are often inadequately described and inadequately applied
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“All randomised CSOs will be included in the statistical analyses, that is, an intention-to-treat analysis will be used.61”
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“We replaced mention of “intention to treat” analysis, a widely misused term, by a more explicit request for information about retaining participants in their original assigned groups [26].”
From CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials (2010) · cites this paper as [26]
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“In an analysis of randomized controlled trials reported as using intent-to-treat analyses, Hollis and Campbell (1999) note that there is no standard definition of intent-to-treat and researchers vary widely in their interpretation.”
From Do growth mindset interventions impact students’ academic achievement? A systematic review and meta-analysis with recommendations for best practices. (2023) · cites this paper as Hollis and Campbell (1999)
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“None of the studies performed a full intention-to-treat analysis according to the definition of intention-to-treat given by Hollis and Campbell [38]”
From Internet-based physical activity interventions: a systematic review of the literature. (2007) · cites this paper as [38]
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“However, a full application of the intent-to-treat model according to the definition given by Hollis and Campbell [38] may not be possible for most physical activity studies because, in most of these studies, there will be at least some subjects who drop out, refuse to complete final assessments, or change residence.”
From Internet-based physical activity interventions: a systematic review of the literature. (2007) · cites this paper as [38]
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Metadata
- Authors
- Hollis, S., & Campbell, F.
- Affiliations
- Lancaster University (GB)
- AstraZeneca (United Kingdom) (GB)
- Corresponding author
- Hollis, S.
- ORCID
- Campbell, F.
- Venue
- BMJ
- Publisher
- BMJ
- Published
- 1999-09-11
- Volume
- 319
- Issue
- 7211
- Pages
- 670-674
- ISSN
- 0007-1447 (ISSN-L)
- 0959-8138
- 1468-5833
- PMC
- PMC28218
- OpenAlex
- W1984052453
- Cited by
- 2,160
- References
- 67
- Citations by year
- 2026: 32 · 2025: 42 · 2024: 40 · 2023: 67 · 2022: 68 · 2021: 66 · 2020: 78 · 2019: 82 · 2018: 74 · 2017: 73 · 2016: 106 · 2015: 107 · 2014: 144 · 2013: 128 · 2012: 128
- FWCI
- 7.30
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- BMJ (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Research Explorer (The University of Manchester) (submittedVersion)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Physical Sciences › Mathematics › Statistics and Probability › Advanced Causal Inference Techniques
- Keywords
- intention-to-treat analysis, randomized controlled trials, methodological quality, missing data, bias in treatment effect estimation, reporting practices, medical journals
- MeSH terms
- Data Collection, Decision Making, Randomized Controlled Trials as Topic, Treatment Refusal, Treatment Outcome, Patient Selection
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