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Experience of assessing RCT funding applications to the Medical Research Council (MRC) & National Institute for Health Research (NIHR) highlighted that the selection of the target difference (‘effect size’) was a key area of uncertainty in trial design.1 Proposals that used inappropriately large effect sizes were not uncommon. To address this problem, the MRC-NIHR Methodology Research Programme’s Advisory Group invited proposals for a Methodology State-of-the-Art Workshop to develop guidance on this aspect of trial design.


The DELTA2 project objectives are:

  1. Review the existing guidance provided by funders to researchers and panel/board members;
  2. Identify any key methodological developments or changes in practice since a comprehensive review was undertaken and update method guidance;
  3. Determine the scope of the guidance that would aid researchers and address funders’ needs;
  4. Achieve consensus on structured guidance for choosing the target difference; and
  5. Identify future research needs.

To achieve these objectives, multiple stages of research will be carried out. We plan to review the relevant guidance provided by UK and international funders of randomised trials. We will also systematically review recent methodological developments regarding methods for determining the target difference in randomised controlled trials.

We will then undertake a Delphi process involving key stakeholders to assess their views on the required scope and focus of the guidance. The Delphi process will incorporate a two-day workshop of key stakeholders to help us achieve consensus.


Guidance is currently under development. We intend to present study preliminary guidance findings at the joint PSI and International Clinical Trials Methodology conference in May 2017. Additional feedback from key stakeholders who participated in the Delphi process will be sought. We plan to finalise and publish the guidance in the summer of 2017.


  1. Cook JA, Julious SA, Sones W, Rothwell JC, Ramsay CR, Hampson LV, Emsley R, Walters SJ, Hewitt C, Bland MJ, Fergusson DA, Berlin J, Altman D, Vale LD. Choosing the target difference ("effect size") for a randomised controlled trial - DELTA2 guidance protocol. Trials. 2017; 18: 271.