🪵Intro to Demographic Methods Unit 5 – Mortality Measures and Trends

Key Concepts and Definitions

• Mortality refers to the occurrence of death in a population
• Crude death rate (CDR) measures the number of deaths per 1,000 population in a given year
• Age-specific mortality rates (ASMR) calculate the number of deaths per 1,000 population for specific age groups
• Life expectancy at birth (e0) represents the average number of years a newborn is expected to live given current mortality conditions
• Infant mortality rate (IMR) measures the number of deaths among infants under one year old per 1,000 live births
• Neonatal mortality rate (NMR) focuses on deaths occurring within the first 28 days of life
• Under-five mortality rate (U5MR) captures the probability of dying between birth and the fifth birthday
• Cause-specific mortality rates analyze deaths attributed to specific causes (cardiovascular diseases, cancers, etc.)

Measures of Mortality

• Crude death rate (CDR) provides a general overview of mortality in a population but does not account for age structure differences
• Age-specific mortality rates (ASMR) offer a more detailed understanding of mortality patterns across different age groups
  • ASMRs are calculated by dividing the number of deaths in a specific age group by the population in that age group and multiplying by 1,000
• Infant mortality rate (IMR) is a sensitive indicator of overall health and socioeconomic conditions in a population
• Life expectancy at birth (e0) summarizes the mortality experience of a population and allows for comparisons across populations and time periods
• Cause-specific mortality rates help identify leading causes of death and inform public health interventions
• Maternal mortality ratio (MMR) measures deaths related to pregnancy and childbirth per 100,000 live births
• Potential years of life lost (PYLL) quantifies premature mortality by considering the age at which deaths occur

Life Tables and Their Components

• Life tables are statistical tools that summarize the mortality experience of a population
• Cohort life tables follow a specific group of individuals born in the same year throughout their lifetime
• Period life tables represent the mortality experience of a hypothetical cohort subjected to current age-specific mortality rates
• Key components of a life table include:
  • Age interval (x to x+n)
  • Probability of dying (qx) within the age interval
  • Number of survivors (lx) at the beginning of each age interval
  • Number of deaths (dx) within each age interval
  • Person-years lived (Lx) within each age interval
  • Total number of person-years lived (Tx) beyond age x
  • Life expectancy (ex) at age x
• Abridged life tables aggregate age intervals (0, 1-4, 5-9, etc.) while complete life tables use single-year age intervals

Age-Specific Mortality Rates

• Age-specific mortality rates (ASMR) measure the number of deaths per 1,000 population in a specific age group
• ASMRs are calculated as: $ASMR = \frac{Deaths in age group x}{Population in age group x} \times 1,000$
• ASMRs reveal distinct mortality patterns across the life course
  • High rates in infancy, low rates in childhood and early adulthood, increasing rates in later adulthood
• Age-specific mortality curves display the relationship between age and mortality risk
• Lexis diagrams are used to visualize age-specific mortality rates over time and across cohorts
• Decomposition methods attribute changes in life expectancy to changes in age-specific mortality rates
• ASMRs are used to construct life tables and calculate summary measures like life expectancy

Standardization Techniques

• Standardization techniques allow for the comparison of mortality rates across populations with different age structures
• Direct age standardization applies a standard population's age structure to the age-specific mortality rates of the populations being compared
  • Directly standardized mortality rate (DSMR) = $\sum_{x=0}^{\omega} \frac{ASMR_x \times Standard Population_x}{Total Standard Population}$
• Indirect age standardization applies the age-specific mortality rates of a standard population to the age structure of the population being studied
  • Standardized mortality ratio (SMR) = $\frac{Observed Deaths}{Expected Deaths} \times 100$
• Choice of standard population can impact the results of standardization
• Standardization techniques do not eliminate the effect of age structure but rather control for it to enable meaningful comparisons

Trends in Global Mortality

• Global life expectancy has increased dramatically over the past century due to improvements in living conditions, healthcare, and disease control
• Disparities in mortality persist across regions, countries, and socioeconomic groups
• Epidemiological transition theory describes the shift from high mortality due to infectious diseases to lower mortality from chronic and degenerative diseases
• Demographic transition theory links changes in mortality and fertility to modernization and economic development
• Double burden of disease refers to the coexistence of both communicable and non-communicable diseases in low- and middle-income countries
• Health transition encompasses broader social, cultural, and behavioral determinants of health and mortality
• Compression of morbidity hypothesis suggests that the onset of chronic diseases can be postponed to later ages, reducing the duration of morbidity before death

Data Sources and Collection Methods

• Vital registration systems are the primary source of mortality data in many countries
  • Vital registration records births, deaths, marriages, and divorces
  • Completeness and accuracy of vital registration data vary across countries
• Population censuses provide denominators for calculating mortality rates and can include questions on household deaths
• Sample registration systems (SRS) continuously enumerate vital events in a representative sample of the population (India's Million Death Study)
• Demographic surveillance sites (DSS) longitudinally monitor populations in defined geographic areas to capture vital events (INDEPTH Network)
• Verbal autopsy (VA) methods gather information about the cause of death through interviews with family members or caregivers in settings lacking medical certification
• Indirect estimation techniques (Brass methods, sibling survival methods) are used to estimate mortality in the absence of complete vital registration data
• International organizations (WHO, UN Population Division) compile and disseminate mortality data from various sources

Practical Applications and Case Studies

• Monitoring progress towards Sustainable Development Goal (SDG) targets related to mortality (SDG 3: Good Health and Well-being)
• Evaluating the impact of public health interventions on mortality (vaccination programs, safe motherhood initiatives)
• Forecasting future mortality trends for population projections and planning (UN World Population Prospects)
• Assessing the burden of disease and setting health policy priorities (Global Burden of Disease Study)
• Investigating socioeconomic and geographic inequalities in mortality (urban-rural differentials, income gradients)
• Studying the mortality impact of specific events or exposures (natural disasters, famines, pandemics)
• Comparing the effectiveness of different healthcare systems in reducing mortality (cross-national studies)
• Examining the relationship between mortality and other demographic processes (fertility, migration)