So you want to conduct a cluster randomized controlled trial? Lessons from a national cluster trial of early labour

Summary As the discipline of health services research has developed so methods of evaluation have become increasingly sophisticated; where once a ‘simple’ randomized controlled trial would have been considered the gold standard, now terms such as ‘complex interventions’ and the ‘cluster randomized controlled trial’ are hot topics for discussion. The challenges involved in carrying out such studies are rarely presented. In this paper we discuss some of these challenges in relation to ethical and statistical considerations, and illustrate them using a recently completed cluster randomized controlled trial of a decision tool for early labour.