Composite Outcome

What It Is

When outcomes are of interest but are rare, they are combined into one “yes/no” category to create a general outcome that is more frequent. That is, as soon as one of the outcomes occurs, the composite outcome changes from “no” to “yes.”

Why It’s Important

The advantage to investigators conducting a randomized trial is that the composite outcome will require fewer patients for the same statistical power to find a difference between study groups than if each rare outcome were analyzed separately.

Caveat: many times the composite outcome’s results are heavily influenced by one of the components that is more common than the others. For example, a composite outcome with recurrent percutaneous coronary intervention (PCI), myocardial infarction, stroke, death. The PCI will be much more common than the other outcomes. If differences in the composite outcome are seen, it may only be because of the PCI and not because of changes in myocardial infarction, stroke or death.