Foundation Health Measures – Technical Notes

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Quality and Years of Life 

Measuring Life Expectancy

Life expectancy is defined as the average number of years a group of persons are expected to survive from a given starting age. Life expectancy is calculated based on the mortality data contained in a life table. There are two types of life tables: the cohort (or generation) life table and the period (or current) life table. The cohort life table presents the mortality experience of a particular birth cohort (for example, all persons born in the year 1900) from birth throughout their lives. The cohort life table is based on age-specific death rates observed throughout the lifetimes of the cohort members and reflects the mortality experiences of an actual population from birth until the final group member has died (1). 

The period table presents what would happen to a hypothetical cohort if it experienced, throughout its entire life, the mortality conditions of a particular period in time. For example, a period life table for 2018 assumes a hypothetical cohort that is subject throughout its lifetime to the age-specific death rates that occurred in 2018 (1). The period table is used to construct the life expectancies and healthy life expectancies tracked in Healthy People 2020 (HP2020). The methodology for constructing period life tables for the United States has been published in the Technical Notes of the National Vital Statistics Report “United States Life Tables, 2018.” 

Measuring Years of Healthy Life

Due to the multidimensional nature of health, assessing years of healthy life is more complex than measuring life expectancy, and the field is still evolving. Various measures are used nationally and internationally to measure the health component of expected years of healthy life (2). These fall into the following general categories:

  • Assessments of overall health status by individuals or their proxies.
  • Measures that address individual aspects of health such as the existence of chronic conditions or aspects of functional limitation.
  • Composite measures that include multiple dimensions of health. Scores on the various dimensions are combined into a single measure using a predetermined algorithm.

Measures that combine mortality and morbidity (where the morbidity measure can be either of the types described above or a measure of a single dimension of health) use years as the metric to quantify healthy life.

The healthy life measures used in HP2020 are defined as follows:

  • Expected years of life in good or better health is the average number of years a person can expect to live in good or better health. This measure assesses healthy life using a single global assessment question that asks a person or their proxy to rate their health as “excellent,” “very good,” “good,” “fair,” or “poor.”
  • Expected years of life free of activity limitation is the average number of years a person can expect to live free from a limitation in activities, a need for assistance with personal or routine care needs, or a need to use special equipment.
  • Expected years of life free of disability is the average number of years a person can expect to live without having difficulty in any of the six domains of functioning: hearing; seeing; concentrating, remembering, or making decisions; walking or climbing stairs; dressing or bathing; and doing errands alone.

Computing Healthy Life Measures

Healthy life expectancies are calculated using a period life table methodology (1). Age-specific mortality rates are combined with age-specific prevalence rates for the specific health component to produce an estimate of overall healthy life expectancy. This methodology has been published elsewhere (3). Healthy life expectancies can be compared across populations, as well as over time, as long as the age-specific prevalence rates are reliable across all age categories.

Data Items Used for Healthy Life Measures

  • Respondent-assessed health status is measured by the single question in which the respondent or proxy respondent is asked to rate their health as “excellent,” “very good,” “good,” “fair,” or “poor.” This self-assessed health rating has been validated as a useful indicator of a person’s actual health for a variety of populations, permitting broad comparisons across different conditions and populations (4).
  • Activity limitation is measured using questions about personal care needs, limitations of activities, and use of special equipment. Adults are asked whether they need assistance with personal care needs, such as eating, bathing, dressing, or getting around inside the home; if they need assistance with routine care needs, such as household chores; if they have mental or physical problems that prevent them from working at a job or going to school; or if they have health problems that require the use of special equipment, such as a cane, wheelchair, or special telephone. Respondents (or their proxies) responding “yes” to any of these questions are classified as having an activity limitation.
  • Disability status is measured using a set of six questions developed for the American Community Survey (ACS). These questions ask if a person has difficulty in six domains of functioning: hearing; seeing; concentrating, remembering, or making decisions; walking or climbing stairs; dressing or bathing; and doing errands alone. The hearing and seeing questions are asked of persons aged 1 year and over. Questions on concentrating, remembering, or making decisions; questions on walking or climbing stairs; and questions on dressing or bathing are asked of persons aged 5 years and over. The questions on doing errands alone are asked of persons aged 15 years and over. Respondents (or their proxies) who answer “yes” to one or more of the questions are classified as being “at risk” of having a disability. Beginning in 2018, the set of six ACS disability questions were no longer included in the National Health Interview Survey. Consequently, the Foundation Health Measures that include disability (FHM-1.2, 2.2, 6.1, 6.2) show data only through 2017.

References

  1. Arias E, Xu JQ. United States life tables, 2018. National Vital Statistics Reports; vol 69 no 12. Hyattsville, MD: National Center for Health Statistics. 2020. Available from: https://www.cdc.gov/nchs/data/nvsr/nvsr69/nvsr69-12-508.pdf.
  2. Murray CJL, Salomon JA, Mathers CD, Lopez AD, editors. Summary Measures of Population Health: Concepts, ethics, measurement, and applications. Geneva, Switzerland: World Health Organization. 2002.
  3. Molla MT, Madans JH, Wagener DK, Crimmins EM. Summary Measures of Population Health: Report of findings on methodologic and data issues. National Center for Health Statistics. Hyattsville, MD. 2003. Available from: https://www.cdc.gov/nchs/data/misc/pophealth.pdf.
  4. Idler EL, Benyamini Y. Self-rated Health and Mortality: A review of twenty-even community studies. J Health Soc Behav38:21–37. 1997.