Use of Composite Outcomes in Neonatal Trials: An Analysis of the Cochrane Reviews

INTRODUCTION: Composite outcomes are used to increase the power of a study by combining event rates. Many composite outcomes in adult clinical trials have components that differ substantially in patient importance, event rate, and effect size, making interpretation challenging. Little is known about the use of composite outcomes in neonatal randomized controlled trials (RCTs).

METHODS: We assessed the use of composite outcomes in neonatal RCTs included in Cochrane Neonatal reviews published till November 2017. Two authors reviewed the components of the composite outcomes to compare their patient importance and computed the ratios of effect sizes and event rates between the components, with an a priori threshold of 1.5, indicating a substantial difference. Descriptive statistics were presented.

RESULTS: We extracted 7,766 outcomes in 2,134 RCTs in 312 systematic reviews. Among them, 55 composite outcomes (0.7%) were identified in 46 RCTs. The vast majority (92.7%) of composite outcomes had 2 components, with death being the most common component (included 51 times [92.7%]). The components in nearly three-quarters of the composite outcomes (n = 40 [72.7%]) had different patient importance, while the effect sizes and event rates differed substantially between the components in 27 (49.1%) and 35 (63.6%) outcomes, respectively, with up to 43-fold difference in the event rates observed.

CONCLUSIONS: The majority of composite outcomes in neonatal RCTs had different patient importance with contrasting effect sizes and event rates between the components. In patient communication, clinicians should highlight individual components, rather than the composites, with explanation on the relationship between the components, to avoid misleading impression on the effect of the intervention. Future trials should report the estimates of all individual components alongside the composite outcomes presented.