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Practical help for specifying the target difference in sample size calculations for RCTs: the DELTA(2) five-stage study, including a workshop

Cook, JA; Julious, SA; Sones, W; Hampson, LV; Hewitt, C; Berlin, JA; Ashby, D; ... Vale, LD; + view all (2019) Practical help for specifying the target difference in sample size calculations for RCTs: the DELTA(2) five-stage study, including a workshop. Health Technology Assessment , 23 (60) pp. 1-88. 10.3310/hta23600. Green open access

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Abstract

Background: The randomised controlled trial is widely considered to be the gold standard study for comparing the effectiveness of health interventions. Central to its design is a calculation of the number of participants needed (the sample size) for the trial. The sample size is typically calculated by specifying the magnitude of the difference in the primary outcome between the intervention effects for the population of interest. This difference is called the ‘target difference’ and should be appropriate for the principal estimand of interest and determined by the primary aim of the study. The target difference between treatments should be considered realistic and/or important by one or more key stakeholder groups. / Objective: The objective of the report is to provide practical help on the choice of target difference used in the sample size calculation for a randomised controlled trial for researchers and funder representatives. / Methods: The Difference ELicitation in TriAls2 (DELTA2) recommendations and advice were developed through a five-stage process, which included two literature reviews of existing funder guidance and recent methodological literature; a Delphi process to engage with a wider group of stakeholders; a 2-day workshop; and finalising the core document. / Results: Advice is provided for definitive trials (Phase III/IV studies). Methods for choosing the target difference are reviewed. To aid those new to the topic, and to encourage better practice, 10 recommendations are made regarding choosing the target difference and undertaking a sample size calculation. Recommended reporting items for trial proposal, protocols and results papers under the conventional approach are also provided. Case studies reflecting different trial designs and covering different conditions are provided. Alternative trial designs and methods for choosing the sample size are also briefly considered. / Conclusions: Choosing an appropriate sample size is crucial if a study is to inform clinical practice. The number of patients recruited into the trial needs to be sufficient to answer the objectives; however, the number should not be higher than necessary to avoid unnecessary burden on patients and wasting precious resources. The choice of the target difference is a key part of this process under the conventional approach to sample size calculations. This document provides advice and recommendations to improve practice and reporting regarding this aspect of trial design. Future work could extend the work to address other less common approaches to the sample size calculations, particularly in terms of appropriate reporting items. / Funding: Funded by the Medical Research Council (MRC) UK and the National Institute for Health Research as part of the MRC–National Institute for Health Research Methodology Research programme.

Type: Article
Title: Practical help for specifying the target difference in sample size calculations for RCTs: the DELTA(2) five-stage study, including a workshop
Open access status: An open access version is available from UCL Discovery
DOI: 10.3310/hta23600
Publisher version: https://doi.org/10.3310/hta23600
Language: English
Additional information: © Queen’s Printer and Controller of HMSO 2019. This work was produced by Cook et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK.
Keywords: Science & Technology, Life Sciences & Biomedicine, Health Care Sciences & Services, CLINICALLY IMPORTANT DIFFERENCE, CLUSTER RANDOMIZED-TRIALS, QUALITY-OF-LIFE, COST-EFFECTIVENESS ANALYSIS, EXPECTED VALUE, MACULAR HOLE, ARTERIAL REVASCULARIZATION, CHRONIC RHINOSINUSITIS, OCULAR HYPERTENSION, POWER CALCULATIONS
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Inst of Clinical Trials and Methodology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Inst of Clinical Trials and Methodology > MRC Clinical Trials Unit at UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10085926
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