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Choosing the target difference (‘effect size’) for a randomised controlled trial - DELTA2 guidance protocol

Overview of attention for article published in Trials, June 2017
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Title
Choosing the target difference (‘effect size’) for a randomised controlled trial - DELTA2 guidance protocol
Published in
Trials, June 2017
DOI 10.1186/s13063-017-1969-5
Pubmed ID
Authors

Jonathan A. Cook, Steven A. Julious, William Sones, Joanne C. Rothwell, Craig R. Ramsay, Lisa V. Hampson, Richard Emsley, Stephen J. Walters, Catherine Hewitt, Martin Bland, Dean A. Fergusson, Jesse A. Berlin, Doug Altman, Luke D. Vale

Abstract

A key step in the design of a randomised controlled trial (RCT) is the estimation of the number of participants needed. By far the most common approach is to specify a target difference and then estimate the corresponding sample size; this sample size is chosen to provide reassurance that the trial will have high statistical power to detect such a difference between the randomised groups (at the planned statistical significance level). The sample size has many implications for the conduct of the study, as well as carrying scientific and ethical aspects to its choice. Despite the critical role of the target difference for the primary outcome in the design of an RCT, the manner in which it is determined has received little attention. This article reports the protocol of the Difference ELicitation in TriAls (DELTA(2)) project, which will produce guidance on the specification and reporting of the target difference for the primary outcome in a sample size calculation for RCTs. The DELTA(2) project has five components: systematic literature reviews of recent methodological developments (stage 1) and existing funder guidance (stage 2); a Delphi study (stage 3); a 2-day consensus meeting bringing together researchers, funders and patient representatives, as well as one-off engagement sessions at relevant stakeholder meetings (stage 4); and the preparation and dissemination of a guidance document (stage 5). Specification of the target difference for the primary outcome is a key component of the design of an RCT. There is a need for better guidance for researchers and funders regarding specification and reporting of this aspect of trial design. The aim of this project is to produce consensus based guidance for researchers and funders.

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Geographical breakdown

Country Count As %
Unknown 53 100%

Demographic breakdown

Readers by professional status Count As %
Other 8 15%
Student > Ph. D. Student 7 13%
Student > Doctoral Student 5 9%
Researcher 5 9%
Professor 4 8%
Other 8 15%
Unknown 16 30%
Readers by discipline Count As %
Medicine and Dentistry 18 34%
Pharmacology, Toxicology and Pharmaceutical Science 3 6%
Nursing and Health Professions 3 6%
Neuroscience 3 6%
Psychology 3 6%
Other 6 11%
Unknown 17 32%