Population Health Metrics Consuelo Quispe MD. | Social Epidemiology | RECETOX Author is licensed under Objectives By the end of the session, students should understand: • Purpose of different health indicators • Main health indicators used in public/population health • Selected features and findings of the Global Burden of Disease (GBD) program • Health outcomes used in the GBD • Conditions accounting for most ill health burden • Risk factors responsible for ill health • Next class • Absolute vs. relative inequalities of health What are the steps to improve health? Think about one health issue and how to address it. Steps to improve health Measure the outcome of interest/track changes in health and disease Identify/understand causal factors Assess what health and social programs will provide greatest gains for healthy life Design and implement interventions Evaluate the interventions (measure the outcome of interest) Step 1: Measure the outcome • Find appropriate indicators to measure, estimate or quantify: • health and disease in population(s) • risk factors/determinants • attribution of ill health to risk factors/determinants • Sometimes “big brush” picture • Largely based on routinely available data • Often combining data from various sources • Crucial for policy decisions, priority setting, design of interventions, evaluation of interventions “Conventional” measures • Prevalence of a disease/exposure • Incidence of a disease • Mortality • all causes vs. causespecific rates • all ages vs. agespecific rates • Life expectancy • At birth • At a specific age Life expectancy: assumptions • ‘Period life tables’ unrealistically assume mortality will stay the same in the future. • Life expectancy has been growing at around 3 months a year for decades, corresponding to the annual risk of death reducing by about 2% per year. • ‘cohort life’ makes various projections about whether these trends will continue in the future. https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/lifeexpectancies/methodologies/periodandcohortlifeexpectancyexplained#difference-between-period-and-cohort- life-expectancies https://webarchive.nationalarchives.gov.uk/ukgwa/20160105221532/http://www.ons.gov.uk/ons/rel/lifetables/historic-and-projected-data-from-the-period-and-cohort-life-tables/2012-based/stb-2012- based.html From partial measures to summary measures Molla MT, Wagener DK, Madans JH. Summary measures of population health: methods for calculating healthy life expectancy. Healthy People 2010 Stat Notes. 2001 Aug;(21):1-11. doi: 10.1037/e583762012-001. PMID: 11676467. From partial measures to summary measures From Field & Gold, 1998 Life paths Morbidity compression (rectangularisation) Compression of morbidity hypothesis. Fries, 1998 Healthy life expectancy (HALE) • Healthy life expectancy or health-adjusted life expectancy (HALE) measures the number of years that a person at a given age can expect to live in good health, accounting for mortality and disability. • Equals to the average number of years a newborn can expect to live “full”. In other words, not hampered by disabling illnesses or injuries • Summarizes mortality and nonfatal outcomes in a single measure of average population health • Can compare health between countries or measure changes over time • Can inform policy questions dependent on how morbidity changes as mortality decrease. Healthy life expectancy at birth by country, 2010 The Lancet 2012 380, 2144 2162 A Male healthy life expectancy (A) and female healthy life expectancy (B). Global Burden of Diseases (GBD) • “Global descriptive epidemiology” • Systematic, scientific effort to quantify the comparative magnitude of health loss due to diseases, injuries, and risk factors by: • age • sex • geographies • specific points in time • Compare the effects of different diseases that kill people prematurely and cause ill health and disability. • GBD was established by WHO, WB, and Harvard in 1996, currently led by the Institute for Health Metrics and Evaluation (IHME), University of Washington. • https://vizhub.healthdata.org/gbd-compare/ GBD metrics • All cause mortality • Deaths by cause • Years of life lost (YLLs) • Years lived with disability (YLDs) • Disability-adjusted life years (DALYs) for • Comprehensive list (2013) • 291 causes of diseases and injuries • 67 risk factors The Disability-Adjusted Life Years (DALY) • A summary measure that combines time lost through premature death and time lived in states of less than optimal health, loosely referred to as “disability”. • One DALY can be thought of as one year of ‘healthy’ life lost. • Combines the years of life lost through: • premature death • years of healthy life lost through disability. • DALYs lost = Years of healthy life lost. • If everybody in a population lived to 80 completely healthy, then there would be zero DALYs Source: The Global Burden of Disease: Generating Evidence, Guiding Policy (GBD 2010) YLL and YLD composition of total DALYs by region, 2010 Calculating DALYs 1 Classify all disease and conditions into 107 categories in 3 groups and assign into 7 disability classes weighted from 0 (perfect health) to 1 (death). 2 Assign all deaths to a category by age, sex and region 3 Calculate years of life lost per death 4 Estimate all cases of disability by age, sex , region, severity (disability class) and duration (years of healthy life lost) until remission or death 5 Combine all deaths and disability losses by cause, age, sex and region 6 Allow a discount rate of 3% so future years of healthy life are valued at progressively lower levels 7 Weight years of life lost at different relative values less for children and aged, more for adults (maximum value at age 25) 8 Sum all DALYS to obtain the Global Burden of Disease Examples of mean disability weights (2004) • AIDS 0.505 • Infertility 0.180 • TB 0.272 • Blindness 0.600 • Diabetes 0.015 • Depression 0.399 • Alzheimer’s 0.666 • Angina 0.141 • Deafness 0.234 https://ghdx.healthdata.org/gbd-2019 Trends in DALYs from 1990 to 2015 by cause The Lancet 2016 388, 1603 1658 Incorporating risk factors • Comparative risk assessment ( CRA ) approach, developed by Murray and Lopez ( Epidemiol ., 1999) • Conceptual framework for population risk assessment across risks and over time. • Evaluates how much of the burden of disease observed in a given year can be attributed to past exposure to a risk factor. • Attributable burden is estimated by comparing observed health outcomes to those that would have been observed had a counterfactual level of exposure occurred in the past. • Different risks lead to different health outcomes: separate assessments undertaken for specific risk outcome pairs. Global health risks: mortality and burden of disease attributable to selected major risks. https://apps.who.int/iris/bitstrea m/handle/10665/44203/97892 41563871_eng.pdf?sequence =1&isAllowed=y The proportion of global all-cause DALYs attributable to behavioral, environmental and occupational, and metabolic risk factors and their overlaps, by age for both sexes combined in 2013. https://www.thelancet.com/j ournals/lancet/article/PIIS01 40-6736(15)00128- 2/fulltext#figures Summary Different health indicators have different purpose. Conventional indicators remain primary sources of data. GBD metrics extremely influential. DALY widely used but complex and sometimes difficult to interpret.