Researchers combine multiple outcomes to form a composite outcome, either to increase the power of an analysis via increased event rates or due to the 'competing' nature of the components. However, the use of composite outcomes may mislead patients when the components differ substantially in their patient-importance, event rate and effect size.
We assessed how often composite outcomes were incorporated in neonatal trials and how comparable their components were.
We analysed randomised controlled trials (RCTs) in Cochrane Neonatal reviews published up to November 2017 and we extracted up to five outcomes per study. We selected all composite outcomes for further assessment. Two researchers independently determined the patient-importance of the components of a composite outcome, with discussion leading to a consensus. We compared the effect size and event rate between the components, and considered the components to have a substantially different event rate and/or effect size when their ratios were > 1.5.
We identified 2115 RCTs published between 1952 and November 2017 in 311 Cochrane Reviews. We extracted a total of 7621 outcomes and among them we identified 53 composite outcomes (0.70%) in 45 RCTs. There were two components in 49 composite outcomes and more than two components in four outcomes. The components in 34 composite outcomes (64.2%) had clearly different patient-importance, while the effect sizes and event rates differed substantially between the components in 24 (45.3%) and 34 (64.2%) outcomes respectively, with up to a 43-fold difference in the event rates between components.
A small proportion of neonatal RCTs included composite outcomes. However, when they were included, the majority had contrasting effect sizes and event rates between the components, with substantially different patient-importance between components in nearly two-thirds of the outcomes. When the evidence from such trials is used in communication with carers, health care providers should not only present the composite outcome as a whole, but also highlight the individual components sequentially, taking into account the relationship between the components.
Patient or healthcare consumer involvement:
Two authors (newly graduated medics) consulted their lay relatives on the patient-importance of the components during their judgement process.