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How can we design trials in smaller populations?

16 December 2016

How should we approach trial design when we can get some, but not all, of the way to the numbers required for a randomised phase III trial?

This is the question motivating the recent BMC Medicine paper from the Unit's director Max Parmar, with Matt Sydes and Tim Morris.

There are situations when we know we will be unable to get enough patients to design the trial we would like; not through sloppiness or laziness, but because the patient population is relatively small. We then have three choices: throw our hands in the air and give up, do an underpowered trial, or make changes to the design to make the numbers feasible.

Parmar and colleagues present a simple, practical framework for making changes to the design. The framework, which should be worked through iteratively in discussions by the trial design team, argues that our first port of call should always be an attempt to increase the number of patients we can enrol. Having done this as far as possible, they consider approaches to reducing the numbers required. These come under 'commonly considered' and 'less commonly considered' approaches. However, commonly considered does not mean 'better', just as less commonly considered approaches does not mean 'worse'.

Entire smaller populations infographic for methodology

If this sounds like it could help you, have a read. The article is also accompanied by a commentary from Kit Roes, principle investigator of the EU-funded Asterix project which is focusing on designs for rare populations.

The authors would be pleased to hear from trialists who are designing trials in these settings. If this is you, get in touch.