Summary measures of population health combine information on different aspects of health, such as mortality, but also health status, morbidity, functional status (a person’s ability to perform normal daily activities required to meet basic needs, fulfil usual roles and maintain health and well-being), or quality of life. Summary measures of population health combine these aspects into a single number. Key examples are healthy life years (HLYs), quality-adjusted life years (QALYs) and disability-adjusted life years (DALYs).

The health of a population can be described by a variety of indicators. Typical indicators of population health are life expectancy, cause-specific mortality rates, numbers of new and existing cases of specific diseases (i.e. incidence and prevalence), and self-perceived health. Each of these indicators points to one facet of health, i.e., either mortality, morbidity or the impact of diseases on patients’ quality of life. An overall view of a population’s health hence requires the combination of those dimensions. Therefore, there has been a markedly increased interest in the development, calculation and use of so-called summary measures of population health (SMPH). 

SMPHs may be divided into two broad families, i.e. “health expectancies” and “health gaps”. Metrics in each family set off morbidity, quality of life and mortality against time and combine these aspects into a dedicated indicator (e.g. healthy life years, HLY). The result is returned as a single number:

• Health expectancies, such as Healthy Life Years (HLYs) and Quality-Adjusted Life Years (QALYs) represent the number of life years lived in good health or lived without specific diseases or disabilities, respectively. In the calculation of these indicators, years lived in full health are “worth” more than years lived in anything but full health. 
• Health gap measures, such as Disability-Adjusted Life Years (DALY), quantify the difference between the actual health of a population and some stated norm or goal for population health. They therefore represent the number of healthy life years that are lost due to poor health and premature mortality.