Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA2 Guidance

How to cite: 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.; Maclennan, G.; Stallard, N.; Rothwell, J.C.; Bland, M.; Brown, L.; Ramsay, C.R.; Cook, A.; Armstrong, D.; Altman, D.; Vale, L.D. Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA² Guidance. Preprints 2018, 2018080521. https://doi.org/10.20944/preprints201808.0521.v1 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.; Maclennan, G.; Stallard, N.; Rothwell, J.C.; Bland, M.; Brown, L.; Ramsay, C.R.; Cook, A.; Armstrong, D.; Altman, D.; Vale, L.D. Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA2 Guidance. Preprints 2018, 2018080521. https://doi.org/10.20944/preprints201808.0521.v1

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MDPI and ACS Style

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.; Maclennan, G.; Stallard, N.; Rothwell, J.C.; Bland, M.; Brown, L.; Ramsay, C.R.; Cook, A.; Armstrong, D.; Altman, D.; Vale, L.D. Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA² Guidance. Preprints 2018, 2018080521. https://doi.org/10.20944/preprints201808.0521.v1

APA Style

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., Maclennan, G., Stallard, N., Rothwell, J.C., Bland, M., Brown, L., Ramsay, C.R., Cook, A., Armstrong, D., Altman, D., & Vale, L.D. (2018). Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA<sup>2</sup> Guidance. Preprints. https://doi.org/10.20944/preprints201808.0521.v1

Chicago/Turabian Style

Cook, J.A., Doug Altman and Luke David Vale. 2018 "Choosing the Target Difference (“effect size”) for a Randomised Controlled Trial - DELTA<sup>2</sup> Guidance" Preprints. https://doi.org/10.20944/preprints201808.0521.v1

Abstract

The aim of this document is to provide practical guidance on the choice of target difference used in the sample size calculation of a randomised controlled trial (RCT). Guidance is provided with a definitive trial, one that seeks to provide a useful answer, in mind and not those of a more exploratory nature. The term “target difference” is taken throughout to refer to the difference that is used in the sample size calculation (the one that the study formally “targets”). Please see the glossary for definitions and clarification with regards other relevant concepts. In order to address the specification of the target difference, it is appropriate, and to some degree necessary, to touch on related statistical aspects of conducting a sample size calculation. Generally the discussion of other aspects and more technical details is kept to a minimum, with more technical aspects covered in the appendices and referencing of relevant sources provided for further reading.The main body of this guidance assumes a standard RCT design is used; formally, this can be described as a two-arm parallel-group superiority trial. Most RCTs test for superiority of the interventions, that is, whether or not one of the interventions is superior to the other (See Box 1 for a formal definition of superiority, and of the two most common alternative approaches). Some common alternative trial designs are considered in Appendix 3. Additionally, it is assumed in the main body of the text that the conventional (Neyman-Pearson) approach to the sample size calculation of an RCT is being used. Other approaches (Bayesian, precision and value of information) are briefly considered in Appendix 2 with reference to the specification of the target difference.

Supplementary and Associated Material

https://www.csm.ox.ac.uk/research/methodology-research/delta2: DELTA2 project website

Keywords

Target difference, clinically important difference, sample size, guidance, randomised trial, effect size, realistic difference

Subject

Medicine and Pharmacology, Complementary and Alternative Medicine

Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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