 In practice, though, cost-effectiveness analysis in health care allocation faces a substantial methodological hurdle: there is a vast array of incommensurable health improvements—lowering pain levels in arthritis, improving muscle strength or respiration efficiency, controlling high blood pressure, adding a year to life, postponing the onset of dementia. Since CEA requires health improvements to be comparable between individuals and across the population, an underlying health improvement metric—what statisticians call a “latent trait”—needs to be identified that is (at least) ordinal and comparable, if not precisely measurable. We need to identify, in short, what every health improvement shares in common. That is the measure of a health improvement, and the benefit that factors into the CEA calculation.