Estimating Global Burden of Disease

Christopher W. Woods, MD, MPH August 31, 2012

http://www.ted.com/talks/hans_rosling_shows_the_best_stats_you_ve_ever_seen.html

Reliable health data and statistics are the foundation of health policies, strategies, and evaluation and monitoring…….

Evidence is also the foundation for sound health information for the general public.

Margaret Chan 2007

If you are going to work, work on something important

William Foege, 2006

Objectives

• Summarize Measures of Population Health • Describe the Global Burden of Disease Project – Burden of Disease – Burden of Risk • Projecting to the Future

World Population Levels in History

Defining Health

• “ A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity ” WHO Charter, 1948

Measuring Health and Disease

• Rationale (Why) – Assess health status over time – Reduce disease consequence – Application of evidence-based public health practice* • Burden (How) – Frequency (incidence or prevalence) – Severity (premature mortality and extent of disability) – Consequences (health, social, economic) – Type of people affected (gender, age)..disparities

Life Expectancy at Birth, US 1900-2000

• Common metric – Measures average expected age at birth – No measure of quality of life – Strongly affected by infant and childhood mortality Nature Medicine 10, S82 - S87 (2004) www.WorldLifeExpectancy.com

Life Expectancy around the World

Comparing Life Expectancies and Under-Five Mortality Across Countries

Country Gross national income per capita Life expectancy at birth Japan Sweden Singapore United States Mexico China Thailand Uzbekistan Honduras Russia India South Africa Haiti 34,600 36,590 48,520 45,850 10,030 5370 7880 2,020 2,900 10,640 3,460 12,120 1,840 Kenya Malawi 1,170 650 49 41 Botswana 10,250 35

http://www.nytimes.com/2010/08/15/world/asia/15japan.html?_r=1&scp=1&sq=japan%20elderly&st=cse

67 65 61 51 50 82 81 80 77 74 72 70 68 Under-Five Mortality Rates 40 18 74 68 120 4 4 3 7 27 31 21 68 120 125 120

Source: World Health Report 2008 and World Development Group Indicators

Historical Perspective

• As nations become wealthier, they also become healthier, and vice versa.

Source: Marmot M. Health in an Unequal World. The Lancet 2006;368:2081-94.

Swaziland However, this relationship is not linear! In fact, there is a clear inflection point in the curve at

US$5000 per capita

.

Demographic Transition

Transition from traditional to modern society • • Decline in mortality (primarily in under 5) • Lagging decline in fertility http://www.worldlifeexpectancy.

com/world-population-pyramid

The Epidemiologic Transition

• Underlying reasons for the demographic transition – Change in disease pattern • Reduction in malnutrition and communicable diseases

US Crude Mortality Rates for All Causes, Noninfectious Causes, and Infectious Diseases

Armstrong et al, JAMA, 1999.

Components of Public Health Success

• Clean water supply • Sanitary sewage disposal • Food inspection • Disease surveillance • Maternal-child health • Nutrition-free lunch/milk • Housing regulations • Worker safety, ages, hours

Vital statistics: Mortality

• Deaths defined by the Manual of International Statistical Classification of Diseases, Injuries, and Cause of Death, 10 th edition (ICD-10) • Mortality at national and sub-national levels – Fact of death unreliable in 26% of countries (age, sex, place) – Cause is unreliable (even in parts of US) • Supplement with surveys and verbal autopsies Murray et al, 2001

Quality of Death Information

Mathers et al., Bulletin of the World Health Organization, March 2005

Measuring disability

• Morbidity – Case Disability Ratio • Proportion of those diagnosed with a disease who have disability • CDR=1 for most diseases • Latent infection or genetic marker may be <1 – Extent or severity of disability • Usually rank 0 to 1 – Duration • Onset until cure and recovery or death • May have continuing permanent disability

Composite Measures of Population Health

• Health Expectancy=A+

f

(B) – Disability-free Life Expectancy (DFLE) – Health Adjusted Life Expectancy (HALE).

• Health Gap (Healthy Life Lost)=C+

g

(B) – Healthy Life Years (HeaLY) – Disability Adjusted Life Year

A

AGE

B C

Disability Adjusted Life Years (DALY)

• DALY=YLL + YLD (One lost year of healthy life) – YLL=Years of life lost to premature mortality – YLD=Equivalent years of healthy life lost due to disability • Ranges from 0 to 1 • Uses Life Expectancy table – compare with Japan (80 y male, 82.5 female) • Uses health professional expert groups to define values – Discount rates for future life – Weight for life lived at different ages – Disability Weights

DALY: Years of Life Lost (YLL)

• YLL = N x L x YLL=Years of life lost to premature mortality – N=Number of deaths in the population – L x =Standard life expectancy at age of death – X=Age of Death • Example: – 10 deaths at 50 = 10 x L x =10 x 34=340 YLL

Years Lived with Disability

• YLD = I x DW x d – YLD=Years of life lived with disability – I = Number of incident cases in the population – DW = Disability Weight • Scale 0 (perfect health) to 1 (death) – d = Duration of disability (years) • 10 cases of mental retardation due to lead at birth: – 10 x 0.36 x 80 years = 288 YLD

Value Choices for the DALY

• Time discounting: 3% – Falling mortality – Increasing costs • Age weighting – non uniform weights – less weight to years lived at younger and older ages • Disability weights – Largely based on GBD 1990 study with some revisions.

– For local prioritization, may adjust to suit cultural preferences AGE

Effect of discounting and age weights on YLL per Death

Criticisms of the DALY (Policy Perspective)

• Expert vs. community/patient value of health • Discriminates against young and the old • Disabilities additive in nature and could exceed “ 1 ” – More than dead?

• No priority (weight) given to worse off • No prioritization for people with limited treatment potential • Does not assess qualitative difference in outcomes • No Male-Female difference in length of life • Discounting future health outcomes (3% vs. 7%) Adapted from GHEC Module 21 http://globalhealthedu.org/modules/Documents/21/player.html

Global Burden of Disease Study Murray and Lopez, 1996

• Quantified Health effects for 107 diseases and injuries in 8 regions in 1990 • Comprehensive and consistent estimates of morbidity and mortality by age, sex, and region • Introduced the DALY – YLL from premature death and years lived in less than full health

Global Burden of Disease Goals

• Measure loss of health due to comprehensive set of disease injury and risk factor causes in a comparable way • Decouple epidemiological assessment from advocacy • Inject non-fatal health outcomes into health policy debate • Use a common metric for burden of disease assessment using summary measure for population health and cost-effectiveness analysis WHO Global Burden of Disease 2004 Report

GBD Philosophy

• Quantities of interest are total events or states at population levels • Best available data used to make estimates • Corrections for major known biases to improve cross population compatibility • Comprehensive set of disease and injury causes – nothing is left out in principle • No blanks in the tables, only wider uncertainty intervals • Internal consistency used as a tool to improve validity WHO Global Burden of Disease 2004 Report

GBD Data Sources

• Mortality – Death registration, sample registration systems, household surveys, surveillance systems, epidemiological studies, population laboratories • Morbidity/Disability – Disease registers, population-based studies, longitudinal studies, health facility data (injuries)

GBD 2004 Update (2008)

• YLL update by age, sex, and cause for 192 states • YLD estimates for 52 causes • UNAIDS, UNICEF, RBM, IARC, WHO surveillance • Addition of “ refractory errors ” • Revision of “ angina pectoris ” and CVA estimates

Regional Estimates by WHO Region 2004

WHO Global Burden of Disease 2004 Report

Approximate number of data sources, GBD 2004

Mortality-causes of death Death registration for 2001 or 2002 Death registration for earlier Child and adult mortality-other sources Epidemiological studies/registers/HS data, etc.

Group I. Communicable (+) Group II. Non-communicable Group III. Injuries Approximate total datasets used WHO Global Burden of Disease 2004 Report 59 711 535 6,539 2,127 18 10,052

Number of datasets by region, GBD 2004

Asia/Pacific

Death Registration

117 Europe 149 High Income 142 Latin America 286 Middle East and North Africa 46 Sub-Saharan Africa World 30

Child/adult mortality data

118 22 16 122 67 190

Epidemiologic data sources

1,820 971 1,830 1,311 645 2,185 770 535 8,747 WHO Global Burden of Disease 2004 Report

Total sources

2,055 1,142 1,988 1,719 758 2,405 10,052

Methods and data for cause-of-death for 2004, by Region

WHO Global Burden of Disease 2004 Report

Global Cause of Death by Category

• Group I – Communicable plus maternal, perinatal and nutritional conditions • Group II – Non-communicable conditions (eg, heart disease, stroke, cancer) • Group III – Injuries including motor vehicle accidents, homicide, and suicide Murray and Chen, 1995

Group I Group II Group III

58.8 million deaths, 2004

GBD 2004: Leading Causes of Death by Income

WHO Global Burden of Disease 2004 Report

GBD 2004, Death by Age and Region

WHO Global Burden of Disease 2004 Report

GBD 2004, Death by Gender and Category

• Cardiovascular diseases are the leading cause of death.

– 32% women, 27% men • Largest difference among intentional injuries – Twice as high among men

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GBD: Age < 5 years

Malnutrition is an underlying cause of 53% of deaths under 2 years of age.

WHO Global Burden of Disease 2004 Report

Proportional distribution of deaths and YLL by region, 2004

WHO Global Burden of Disease 2004 Report

Global Mortality Projections, 2004 to 2030

WHO Global Burden of Disease 2004 Report

Disease Burden Measured in DALY

4 3 9 6 13 1 11 2 5

Global View of HIV Infection

33 million people living with HIV, 2008

UNAIDS, 2008 Report on the Global AIDS Epidemic

Burden of Disease by Region, 2002

Leading Causes of GBD, 2004



2030

WHO Global Burden of Disease 2004 Report

Coming 2010….A Complete Revision 1990-2005

Implementing a BOD study

• • • • • • • • • • Assess demographics Cause of Death Define disability by cause with input Assess reliability/validity Define social preferences for age weighting, discounting, life expectation Est HLL for each condition and by group Perform sensitivity analysis Consider other variations (region, age, sex) Review policy implications Modify as necessary for setting For policy considerations • • • • Est effectiveness of each intervention under consideration.

Work out costs of interventions Develop Cost-effectiveness ratios to maximize return on healthy life per expenditure Review expected gains of healthy life by age, sex, geographic area and adjust as necessary*

Projected Burden of Disease by Income and Major Causes, 2002 - 2030 Source: Mathers CD and Loncar D (2005)

Updated projections of mortality and burden of disease

, WHO.

Baseline Projections by Category, 2000-2030 and Compared with GBD estimates from 1990-2020

Mathers CD, Loncar D, 2006 Projections of Global Mortality and Burden of Disease from 2002 to 2030. PLoS Med 3(11): e442.

Risks Quantified in GBD

Global Distribution of burden of disease attributable to 20 leading selected risk factors

Disease Risk Factors

Deaths and DALYs due to leading 5 risks

Underweight Unsafe sex Blood pressure Tobacco Alcohol Joint effects Deaths No. % 3.7 6.7% 2.9 5.2% 7.1 12.8% 4.9 8.8% 1.8 3.2% 31% DALYs (M) No. % 137.8 9.5% 91.9 6.3% 64.3 4.4% 59.1 4.1% 58.3 4.0% 25%

QALY and DALY