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
Under-Five
Mortality Rates
Japan
34,600
82
4
Sweden
36,590
81
4
Singapore
48,520
80
3
United States
45,850
77
7
Mexico
10,030
74
27
China
5370
72
31
Thailand
7880
70
21
Uzbekistan
2,020
68
68
Honduras
2,900
67
40
Russia
10,640
65
18
India
3,460
61
74
South Africa
12,120
51
68
Haiti
1,840
50
120
Kenya
1,170
49
120
Malawi
650
41
125
Botswana
10,250
35
120
http://www.nytimes.com/2010/08/15/world/asia/15japan.html?_r=1&scp=1&sq=japan%20elderly&st=cse
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, 10th 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)
• Health Gap (Healthy Life
Lost)=C+g(B)
C
% Surviving
– Disability-free Life Expectancy
(DFLE)
– Health Adjusted Life Expectancy
(HALE).
B
A
– Healthy Life Years (HeaLY)
– Disability Adjusted Life Year
AGE
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 Lx
YLL=Years of life lost to premature mortality
– N=Number of deaths in the population
– Lx =Standard life expectancy at age of death
– X=Age of Death
• Example:
– 10 deaths at 50 = 10 x Lx=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
•
Time discounting: 3%
– Falling mortality
– Increasing costs
•
Age weighting
– non uniform weights
– less weight to years lived at
younger and older ages
•
% Surviving
Value Choices for the DALY
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 crosspopulation 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
59
Death registration for earlier
711
Child and adult mortality-other sources
535
Epidemiological studies/registers/HS data, etc.
Group I. Communicable (+)
6,539
Group II. Non-communicable
2,127
Group III. Injuries
18
Approximate total datasets used
WHO Global Burden of Disease 2004 Report
10,052
Number of datasets by region, GBD 2004
Death
Registration
Child/adult
mortality data
Epidemiologic
data sources
Total sources
Asia/Pacific
117
118
1,820
2,055
Europe
149
22
971
1,142
High Income
142
16
1,830
1,988
Latin America
286
122
1,311
1,719
Middle East and
North Africa
46
67
645
758
Sub-Saharan
Africa
30
190
2,185
2,405
World
770
535
8,747
10,052
WHO Global Burden of Disease 2004 Report
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
• 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 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
Cancer Is The World's Costliest Disease, Says American Cancer Society
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WHO Global Burden of Disease 2004 Report
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
Deaths
No. %
DALYs (M)
No. %
Underweight
3.7
6.7%
137.8
Unsafe sex
2.9
5.2%
91.9
6.3%
Blood pressure
7.1
12.8%
64.3
4.4%
Tobacco
4.9
8.8%
59.1
4.1%
Alcohol
1.8
3.2%
58.3
4.0%
Joint effects
31%
25%
9.5%
QALY and DALY