Many primary studies fail to measure aspects of perceived health and quality of life that are very important to patients. When this is the case, evidence regarding interventions impact on PROs may be much weaker than evidence regarding impact on disease indicators morbidity or mortality. In the extreme, no study may address PROs directly. The careful prior consideration of all patient-important outcomes will highlight what is missing in outcome measurement in the eligible randomized trials and other studies. This omission should be highlighted in the reviews authors’ conclusions as an implication for future research.