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The need for a cultural shift from two-arm to multi-arm RCTS


We need a faster and more efficient way of improving patient outcomes in all disease areas. There is a need for a cultural shift in randomised phase III superiority trials. We propose there be fewer two-arm trials and more trials that incorporate multiple research arms.


Well-designed, well-conducted randomised controlled trials (RCTs) are the most reliable way to collect comparative evidence on efficacy and effectiveness, and drive changes in policy and healthcare. A literature search has shown that ~80% of all trials have only 2 arms. A key problem is their low success rate, defined as a convincing finding that the research treatment is better than the current standard-of-care. New treatments commonly do not work as well as hoped, yet we persist with traditional phase III RCTs, that are both expensive and often take many years. A direct conclusion from the high failure rate is that the information on which phase III trials are designed must be flawed. In planning any 2-arm phase III trial, fundamental uncertainties often remain; for example, whether we have reliably selected the most appropriate dose and/or duration of treatment or, for the academic community, whether other treatments have equal (or greater) priority for being assessed?


An academic RCT should not be seen as a way of assessing a specific treatment, but considered as a central tool to improving outcomes for patients with a particular condition as quickly as possible. Therefore, we argue that many more trials should have more than one research arm.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of 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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Sydes, M.R., Parmar, M.K. The need for a cultural shift from two-arm to multi-arm RCTS. Trials 14 (Suppl 1), O3 (2013).

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