life. Outcome measures that consider both quality and quantity
of life include disability adjusted life years (DALYs), healthy year
equivalents (HYEs), and quality adjusted life years (QALYs), which is
the most common. The QALY combines patient longevity and
individuals’ preferences about different levels of health related
quality of life into a single measure, which, in principle, has
meaning across all areas of health service activity.It is a unit of
measure for survival that accounts for the effects of suboptimal
health status and the resulting limitations in quality of life. It is
usually measured on a scale of 0 (representing death) to 1 (representing
full health). Quality adjustment involves placing a
lower value on time spent with impaired physical and emotional
function than time spent in full health: the greater the
impairment, the lower the value of a particular health state. It is
not realistic to expect an individual to sustain the same quality of
life over time; rather, people move in and out of health states (eg,
a person has a stroke and then recovers). Individual QALYs are
calculated by multiplying the time spent in each health state by
the preference for that health state. These are then summed to
arrive at an overall QALY. In a classic study, Boyle et al used a
utility measure to calculate that treating critically ill infants
weighing 1000–1499 g at birth cost CN $3200 per QALY
gained, whereas treating infants with birth weights of 500–999 g
cost $22 400 per QALY gained.