Composite outcomes seem an attractive method to increase statistical power, but they can mask the effect of treatment
According to international guidelines,1 2 outcome measures in a clinical trial should address the risks and benefits of a treatment, be relevant to patients, and be sufficiently common to make the trial feasible. In an attempt to meet these objectives many investigators select outcomes such as all cause mortality, all hospital admissions, or any adverse event. These outcomes can be thought of as composite outcomes as they combine multiple outcomes that are cause specific. All cause mortality is a popular outcome measure because it is believed to provide the net effect of the treatment, it seems more patient relevant than cause specific mortality, and it provides more outcomes so should increase statistical power. Another common approach to increase power is to use wide case definitions and sensitive tests.