DELTA2 guidance on choosing the target difference and undertaking and reporting the sample size calculation for a randomised controlled trial
Open accessAbstract
A key step in the design of a RCT is the estimation of the number of participants needed in the study. The most common approach is to specify a target difference between the treatments for the primary outcome and then calculate the required sample size. The sample size is chosen to ensure that the trial will have a high probability (adequate statistical power) of detecting a target difference between the treatments should one exist. The sample size has many implications for the conduct and interpretation of the study. Despite the critical role that the target difference has in the design of a RCT, the way in which it is determined has received little attention. In this article, we summarise the key considerations and messages from new guidance for researchers and funders on specifying the target difference, and undertaking and reporting a RCT sample size calculation. This article on choosing the target difference for a randomised controlled trial (RCT) and undertaking and reporting the sample size calculation has been dual published in the BMJ and BMC Trials journals The DELTA 2 (Difference ELicitation in TriAls) project comprised five major components: systematic literature reviews of recent methodological developments (stage 1) and existing funder guidance (stage 2); a Delphi study (stage 3); a two-day consensus meeting bringing together researchers, funders and patient representatives (stage 4); and the preparation and dissemination of a guidance document (stage 5). The key messages from the DELTA 2 guidance on determining the target difference and sample size calculation for a randomised caontrolled trial are presented. Recommendations for the subsequent reporting of the sample size calculation are also provided.
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The DELTA project proposes that the primary outcome should be of relevance to at least one key stakeholder group.
“the DELTA (Difference Elicitation in TriAls) project proposes that the primary outcome should be of relevance to at least one key stakeholder group [61]”
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- Authors
- Cook, J. A., Julious, S. A., Sones, W., Hampson, L. V., Hewitt, C., Berlin, J. A., Ashby, D., Emsley, R., Fergusson, D. A., Walters, S. J., Wilson, E. C. F., Maclennan, G., Stallard, N., Rothwell, J. C., Bland, M., Brown, L., Ramsay, C. R., Cook, A., Armstrong, D., Altman, D., & Vale, L. D.
- Affiliations
- Nuffield Orthopaedic Centre (GB)
- University of Sheffield (GB)
- Novartis (Switzerland) (CH)
- University of York (GB)
- Johnson & Johnson (United States) (US)
- Imperial College London (GB)
- King's College London (GB)
- Ottawa Hospital Research Institute (CA)
- University of Aberdeen (GB)
- University of Warwick (GB)
- MRC Clinical Trials Unit at UCL (GB)
- University of Southampton (GB)
- Newcastle University (GB)
- Corresponding author
- Cook, Jonathan A.
- ORCID
- Venue
- Trials
- Published
- 2018-11-05
- Volume
- 19
- Issue
- 1
- Pages
- 606-606
- ISSN
- 1745-6215 (ISSN-L)
- PMC
- PMC6218987
- OpenAlex
- W2899988464
- Cited by
- 197
- References
- 31
- Citations by year
- 2026: 5 · 2025: 14 · 2024: 13 · 2023: 16 · 2022: 24 · 2021: 28 · 2020: 78 · 2019: 14 · 2018: 4
- FWCI
- 25.73
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Trials (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, other-oa)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- White Rose Research Online (University of Leeds, The University of Sheffield, University of York) (acceptedVersion)
- UEA Digital Repository (University of East Anglia) (acceptedVersion)
- Warwick Research Archive Portal (University of Warwick) (acceptedVersion)
- ePrints Soton (University of Southampton) (acceptedVersion)
- LSHTM Research Online (London School of Hygiene and Tropical Medicine) (acceptedVersion)
- Aberdeen University Research Archive (Aberdeen University) (submittedVersion)
- uO Research (University of Ottawa) (submittedVersion, public-domain)
- Apollo (University of Cambridge) (submittedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Lancaster EPrints (Lancaster University) (submittedVersion)
- UCL Discovery (University College London) (submittedVersion)
- Research Portal (King's College London) (submittedVersion, cc-by)
- Spiral (Imperial College London) (submittedVersion, cc-by)
- Warwick Research Archive Portal (University of Warwick) (submittedVersion)
- Apollo
- Apollo (cc-by)
- Funders
- Medical Research Council (N/A)
- National Institute for Health Research (N/A)
- 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 › Statistical Methods in Epidemiology
- Keywords
- sample size determination, randomized controlled trials, statistical power, primary outcomes, reporting guidelines, research funding, trial design
- MeSH terms
- Delphi Technique, Humans, Randomized Controlled Trials as Topic, Guidelines as Topic, Sample Size, Research Report, Numbers Needed To Treat
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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
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