[3] Outcomes measures can be patient-reported, or gathered through laboratory tests such as blood work, urine samples etc.
[2] Depending on the design of a trial, outcome measures can be either primary outcomes, in which case the trial is designed around finding an adequate study size (through proper randomization and power calculation).
In clinical trials such measures of direct importance for an individual may be survival, quality of life, morbidity, suffering, functional impairment or changes in symptoms.
For example, the composite measure "Killed or Seriously Injured" is often used in studies of road safety.
It is also possible that composite measures may mask negative treatment effects of truly important outcomes, such as death or cardiovascular events.