DAE

Abstract

I will describe a trial which combined a cluster-randomised design with a cross-over design. The Preterm Infant Parenting (PIP) trial evaluated a nurse-led training intervention delivered to parents of prematurely born babies to help them meet their babies' needs. An individually randomised trial risked extensive "contamination" of parents in the control arm with knowledge of the intervention, so the investigators instead randomised neonatal units. However, neonatal units differ widely, and only 6 neonatal units were available, so a conventional cluster randomised design would have been underpowered. In the selected design, the six neonatal units were randomly allocated to deliver intervention or control to families recruited during a first 6-month period; after a 2-month interval, each unit then delivered the opposite condition to families recruited during a second 6-month period.

I will present the relative precisions of individually randomised, cluster-randomised and cluster-crossover designs, and design issues including the need for a wash-out period to minimise carry-over. The analysis can be conveniently done using cluster-level summaries. I will end by discussing whether cluster-crossover designs should be more widely used.