Summary Measures of Population Health Topics in Public Health April Sung-Il Cho

SMPH: Definition Measures combining information on mortality and non-fatal health outcomes to represent the health of a particular population as a single numerical index. Numerous measures have been suggested: ALE, DFLE, DALYs, HeaLYs, etc.

Uses of SMPH Comparing the health of one population with that of another Monitoring changes in the health of a given population Identifying and quantifying overall health inequalities within populations Providing appropriate and balanced attention to the effects of non-fatal health outcomes on overall population health

Uses of SMPH (continued) Informing debates on priorities for health service delivery and planning Informing debates on priorities for research and development Improving curricula for professional training in public health Analyzing the benefits of health interventions for use in cost-effectivess analyses

Typology of Summary Measures Measures with lower weights for years in poorer health: ALE, DFLE, DALE, YHL, QALE Difference between the actual health and some stated norm or goal

Key Issues Calculation methods Definition and measurement of health status Valuation of health states Values other than health

Calculation Methods Absolute and covariate-independent forms of summary measure –adjustment for age, sex, race, etc Health expectancies –life-table methods –period vs cohort –incidence vs prevalence Health gaps –choice of a target or norm –explicit vs implicit target –loss due to premature mortality: implied target changes with mortality level changes  impossible to compare between communities

Definition and Measurement of Health States Health domains to be measured –Senses, pain, mobility, cognition, functions (social interaction, usual activities) –Self-reported vs observed Examples –ALE: ADL –YHL: activity limitations and perceived general health –QALE: activity restriction –Dementia-free life expectancy: particular diagnosis –DFLE: long-term disability

Valuation of Health States Value of time spent in each state relative to full health and death Dichotomous –arbitrary cutoffs: difficulty in comparison Polytomous Continuous

Values Other Than Health Need explicit incorporation Discount rates for future health Age weights Equity weights (group difference)

Health Expectancies Generic term for summary measures of population health that estimate the expectation of years of life lived in various health states. This includes expectations for specific health states (e.g. disability-free life expectancy) and for “equivalent good health” (e.g. disability- adjusted life expectancy). Health expectancies are measures of the area under the survivorship curve that take into account differential weights for years lived in different health states.

HALE (Health-adjusted life expectancy) General term for health expectancies which estimate the expectation of equivalent years of good health. HALE is calculated for an exhaustive set of health states defined in terms of disability severity. HALEs give a weight of 1 to years of good health, and non-zero weights to at least some other states of less than good health. Healthy life expectancy, Disability-adjusted life expectancy (DALE): Synonym for HALE.

Methods of Calculation Sullivan’s method Multistate life table method Double decrement life table method

Sullivan’s Method Widely used during the1980s and 1990s to estimate disability-free life expectancy and other forms of health expectancy. Requires only a population life table and prevalence data for the health state or health states of interest. Population life table can be constructed for a population using the observed mortality rates at each age for a given time period. Prevalence rates can be obtained readily from cross-sectional health or disability surveys carried out for a population at a point in time. Surveys of this type are carried out regularly in most developed countries. Uses the observed prevalence of disability at each age in the current population (at a given point of time), to divide the hypothetical years of life lived by a period life table cohort at different ages Then calculate years with and without disability.

Health Gaps

DALY

Disability Adjusted Life Years (DALYs) Measures healthy time lost from specific diseases and injuries in a population Comparable and additive across diseases Ex: Broken scapula =.5 DALYs lost Protein deficiency = 2 DALYs lost Based on relatively accessible incidence data (ICD codes)

DALY Calculation (the easiest way) Years of lost life (YLLs) Inputs Life expectancy at age of death Age at death Years lost to disability (YLDs) Inputs Duration of disease/injury Disability weight of disease/injury % long-term cases +

DALY Calculation: an example 1 family dies –10 year old girl –8 year old boy –38 year old mother –42 year old father YLLs from deaths –70 year life expectancy –73 year life expectancy –46 year life expectancy –33 year life expectancy 222 YLLs 2 people injured –45 y/o woman – Spinal cord injury –55 y/o man – fractured rib YLDs from injuries -Duration (36 year LE) * Disability Wt (.725) = 26 YLDs -Duration (.115 years) * Disability Wt (.199) = 0.02 YLDs A Two-Car Collision YLDs += YLDs

DALY Calculations: Adjustments Designed to allow tailoring to local social values and specific applications for the DALYs Age-weighting – weights the life of a 21 year-old (for instance) more heavily than other ages according to societal preferences. Discounting – commonly used in economic analyses, recommended for DALYs if using the outcome measure in such analyses Caused much contention DALYs can be calculated without such adjustments

DALYs and the Global Burden of Disease WHO/World Bank Global Burden of Disease study outlined methodology for DALYs First attempt at a comprehensive picture of global health Ranked diseases according to the number of DALYs Projected rankings to 2020 Quick results –Ranked 9 th in cause of total DALYs in the world in 1990 –Still ranked 9 th in 2000 estimates –Predicted to be ranked 3 rd in 2020

HeaLY

SMPH and Chronic Diseases Measures the Population Burden from Chronic Diseases Health Expectancies Health Gaps