5. PPHS 501: Population Health & Epidemiology - Burden of Disease
FALL 2025 PPHS 501 Population Health & Epidemiology 1
Instructor: Ananya Banerjee, PhD
(she/her)
Assistant Professor
Equity, Diversity, Inclusion and Anti-Racism (EDIAR) Lead
Department of Epidemiology, Biostatistics and Occupational Health
School of Population and Global Health | McGill University
Population: Burden of Disease
Lecture Date: Sept 24, 2025
Content Overview
How to measure burden of disease
Health-Adjusted Life Expectancy (HALEs)
Disability-Adjusted Life Years (DALY)
Years of Life Lost (YLL)
Years Lived with Disability (YLD)
Quality-Adjusted Life Years (QALY)
Highlights from the Global Burden of Disease (GBD) study
WHAT IS HEALTH?
Definition from WHO Charter, 1948:
"A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."
RECALL: WHY MEASURE POPULATION HEALTH?
Purpose of Measurement:
Tracking public health trends across populations in time and space.
Tracking public health trends within populations to identify inequities in health.
Identifying public health priorities to balance health spending towards factors causing the greatest loss of health.
Monitoring progress towards objectives, evaluating impact of public health interventions, and promoting accountability.
HOW TO SUMMARIZE POPULATION HEALTH?
Historical Metrics:
Comparisons of:
Crude Death Rate (CDR)
Disease-specific mortality
Maternal mortality
Infant mortality
Life expectancy
Key Focus for Health Planners:
Value gained from healthcare spending, encompassing both expenditure and returns for the population.
INDICATORS OF POPULATION HEALTH
Leading Metrics:
Up to the 1960s, life expectancy was the primary indicator of population health.
Limitations of life expectancy: does not account for disability.
Development of additional metrics to capture both mortality and disability:
Healthy Life Expectancy (HLE) / Health-Adjusted Life Expectancy (HALE)
Disability Adjusted Life Years (DALYs)
Quality-Adjusted Life Years (QALYs)
INDICATORS OF POPULATION HEALTH - DATA INFORMATICS
Data Sources:
Latest available epidemiological data must be complete and accurate.
Considerations:
Data should be valid, timely, locally derived, and disaggregated by age and sex.
Acknowledgment of under-reporting or underdiagnosis of health conditions.
TWO MAJOR TYPES OF SUMMARY MEASURES
Health Expectancy Measures:
Measures how healthy is a population.
Health Gap Measures:
Measures health importance of specific issues.
HEALTH ADJUSTED LIFE EXPECTANCY (HALE)
Definition:
Indicator of the average number of years an individual is expected to live in a healthy state.
Summary Measure:
Combines both the quantity of life (mortality) and the quality of life (morbidity) into a single measure.
Usage:
Used to measure burden of disease and injury, risk factors, and performance of public health efforts.
Weights quantify the extent of disability (e.g. Weight = 1 for perfect health).
HISTORY OF HALE
Data Compilation:
WHO began compiling HALE data into tables in 1999 using mortality estimates.
Collaboration with the United Nations Population Division (UNPD) for biannual updates across over 180 member states.
Countries often disaggregate HALE data into regions and communities.
USE OF HALE
Applications:
Predict future health service needs.
Evaluate health programs and identify trends worldwide.
Example:
HALE increased by 5.31 years for males and 5.73 years for females globally from 1990 to 2013 due to public health policies.
USE OF HALE TO UNDERSTAND DISPARITIES
Importance:
Identifying racial and ethnic disparities and understanding their existence.
Advocacy for disaggregated data in health analysis.
THE SULLIVAN METHOD
Definition:
Used by WHO to compute HALE, incorporating life expectancy with a weight for each type of disability based on severity.
THINK-PAIR-SHARE ACTIVITY
HALE comparisons based on hypertension and healthy years at different ages and life expectancy metrics.
Engage in discussions about the implications of these comparisons on health outcomes and interventions.
LIFE EXPECTANCY (e0) vs HALE
Characteristics:
Both metrics reflect specific population groups during defined timeframes.
Individual life expectancies can vary from averages and change over time.
Both should be treated as descriptive, not predictive statistics.
HEALTH GAPS - DISABILITY-ADJUSTED LIFE YEARS (DALYs)
Definition:
Measure of health loss associated with diseases or injuries.
Developed for the Global Burden of Disease (GBD) project.
Components of DALYs:
Years of Life Lost (YLL): Related to deaths and standard life expectancy at age of death.
Years Lived with Disability (YLD): Calculated using incident cases, disability weight, and duration.
Example Calculation:
YLL = Number of deaths x Standard life expectancy at age of death
YLD = Number of incident cases x Disability weight x Average duration
DALY = YLL + YLD
HEALTH GAPS - QALYs
Definition:
QALYs measure the improvement or extension of life quality due to medical interventions.
Utility Weights:
Ranges from 0 (death) to 1 (perfect health) using techniques like standard gamble.
Controversies:
Limited sensitivity to compare similar treatments; serious ill health may outweigh the value of being alive, and cultural variances impact perceptions of health.
GLOBAL BURDEN OF DISEASE STUDY (GBD)
Commission:
Initiated by the World Bank in the 1990s.
Objective:
Quantify health loss due to diseases, injuries, and risk factors for specific demographics.
Outcomes:
Helps policymakers understand health system challenges and track trends over time and across populations.
GBD METHODOLOGY
Data Handling:
Involves a collaborative network of researchers and comprehensive data analysis for health metrics.
Visualizations:
Interactive tools and resources for understanding over 1 billion data points to observe trends in health metrics across various parameters.
CONCLUSION
Key Takeaways:
Understanding methodology and assumptions of burden of disease studies is crucial.
Acknowledgment of the subjectivity of DALY and QALY measures in health distribution analysis.
Consideration of regional variations in health metrics when developing health policy.
NEXT CLASS
Transition to epidemiological methods focusing on Indigenous-led Epidemiology for Truth & Reconciliation Week.
Reflection Activity #2 to be discussed.