Centre for Statistics in Medicine

DELTA2 Guidance: Outputs

The DELTA² project aimed to develop guidance for specifying the target difference (or effect size) in the sample size calculation for a randomised clinical trial (RCT). This guidance is aimed at researchers and funders of RCTs. It is hoped that the guidance will help improve the design of future RCTs.

DELTA2 PROJECT

Introduction

Project summary

Project members

Outputs

FULL GUIDANCE

The final DELTA² guidance was published in the NIHR's Health Technology Assessment journal in 2019:

Cook JA, Julious SA, Sones W, Hampson LV, Hewitt C, Berlin JA, Ashby D,  Emsley R, Fergusson DA, Walters SJ, Wilson ECF, MacLennan G, Stallard N, Rothwell JC, Bland M, Brown L, Ramsay CR, Cook A, Armstrong D, Altman D, Vale LD. Practical help for specifying the target difference in sample size calculations for RCTs: the DELTA2 five-stage study, including a workshop. Health Technology Assessment 2019; 23(60).

SUMMARY GUIDANCE

A summary of the DELTA² guidance is freely available in the BMJ and Trials:

Cook JA, Julious SA, Sones W, Hampson LV, Hewitt C, Berlin JA, Ashby D,  Emsley R, Fergusson DA, Walters SJ, Wilson ECF, MacLennan G, Stallard N, Rothwell JC, Bland M, Brown L, Ramsay CR, Cook A, Armstrong D, Altman D, Vale LD. DELTA² guidance on choosing the target difference and undertaking and reporting the sample size calculation for a randomised controlled trial. BMJ 2018; 363. 

Cook JA, Julious SA, Sones W, Hampson LV, Hewitt C, Berlin JA, Ashby D,  Emsley R, Fergusson DA, Walters SJ, Wilson ECF, MacLennan G, Stallard N, Rothwell JC, Bland M, Brown L, Ramsay CR, Cook A, Armstrong D, Altman D, Vale LD. DELTA² guidance on choosing the target difference and undertaking and reporting the sample size calculation for a randomised controlled trial. Trials 2018; 19: 606.

An article collection of all DELTA²-related papers is available in Trials:

Protocol

The DELTA² protocol has been published and is freely available:

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.

Development

A paper on the development of the DELTA² guidance and related findings is freely available in Trials:

Sones W, Julious SA, Rothwell JC, Ramsay CR, Hampson LV, Emsley R, Walters SJ, Hewitt C, Bland M, Fergusson DA, Berlin JA, Altman D, Vale LD, Cook JA. Choosing the target difference ("effect size") for a randomised controlled trial - the development of the DELTA2 guidance. Trials 2018; 19: 542.

Commentary

Bell M. New guidance to improve sample size calculations for trials: eliciting the target difference. Trials 2018; 19: 605.

Review

A review of the target differences in clinical trials published in Trials:

Rothwell J, Julious SA, Cooper CL. A study of target effect sizes in randomised controlled trials published in the Health Technology Assessment journal. Trials 2018; 19: 544. 

DELTA guidance

Preceding the DELTA² project, the DELTA project published guidance on specifying the target difference in the primary outcome of a randomised controlled trial:

Cook JA, Hislop J, Altman DG, Fayers PM, Briggs AH, Ramsay CR, Norrie JD, Harvey IM, Buckley B, Fergusson D, Ford I, Vale LD. Specifying the target difference in the primary outcome for a randomised controlled trial: guidance for researchers. Trials 2015; 16: 12. 

Getting sample size right for clinical trials (news article). NDORMS departmental website; 6 November 2018.

Improving sample size calculation and reporting for randomized trials with DELTA2 guidance (blog post). BMC Blog Network: On Medicine; 6 November 2018.

Raub N. Sample size - what difference matters? Research Design Service Blog; 1 November 2019.