Population Density, Distribution & Structure

Definitions

• Population density measures the number of individuals per unit area, e.g., square kilometers.
• Population distribution refers to how people are organized over space.
• Population structure encompasses the attributes of people in a specified area, both attributed and achieved.

Population Pyramid

• Population pyramid shows gender and age distribution in a population graphically.
• They are helpful for demographic projections and relating population change effects to health and economic development potential.

Demographic Transition

• Demographic projections and their effect on health and economic development are illustrated in Population Pyramid.

Stages of the Demographic Transition: Classic Pyramid Shapes

• Stage 1 (Expanding): High birth rate coupled with rapid population decrease in upward age groups due to high death rates and consequently, short life expectancy.
• Stage 2 (Expanding): Retains a high birth rate, but sees a fall in mortality, with more people living until middle age, leading to a slightly longer life expectancy.
• Stage 3 (Stationary): Declining birth rate accompanied by a low death rate, resulting in more people living to old age.
• Stage 4 (Contracting): Features low birth and mortality, a higher dependency ratio, and longer life expectancy.

Demographic Transition Model

• Stage 1: High Stationary - high birth and death rates, stable or slow increase, disease, famine and poor medical knowledge
• Stage 2: Early Expanding - high birth rates, rapidly falling death rates, very rapid increasing population
• Stage 3: Late expanding - falling birth rates, slower falling death rates, increase slows down
• Stage 4: Low stationary - low birth and death rates, slower increasing population
• Stage 5 (Hypothetical): Declining - very low birth and death rates, population decrease

Critiques of Demographic Transition Theory

• Country-specific conditions impact progression through stages in various ways and orders.
• Legislative actions (China) or ideology (Cuba) cause rapid fertility decline in some countries.
• Unforeseen events, such as the AIDS epidemic in Sub-Saharan Africa, have prevented death rates from declining as initially predicted and no migrations were considered

Health and Mortality

• Health and death are two sides of morbidity and mortality.
• Morbidity is the prevalence of disease in a population.
• Mortality represents the pattern of death.
• Life expectancy gives the average length of life or expected age at death.
• The number of years left at a given age varies and has better predictability as you get older.

Population Surveys

• The National Census is used to collect population data.
• Data collection has time delays.
• Certain persons may not be counted as accurately and not be representative.
  • People on Indigenous reserves
  • Natural disaster victims
  • Armed forces and institutionalized populations in the US
  • Those not responding linked to administrative databases for info

Vital Statistics

• Provinces/territories, births, stillbirths, deaths, marriages are observed
• Deaths are coded according to ICD-10
• The surveys determine cause-specific death, life expectancy/birth rates
• Non-Canadian resident deaths are included
• Limitations: Data could be incomplete or inaccurate

Interview Surveys

• There are some issues with how these surveys are carried out.
• Diagnoses problems: undiagnosed or recall errors
• Participants give alternate answers
• Interviewers record errors or biases

Hospital Data

• Admissions are selective, with focus on:
• Personal characteristics
• Disease severity and associated conditions
• Admission policies
• Hospital records not made for research
• Data is missing, incomplete, illegible
• Diagnostic quality is variable
• Risk populations not defined.

Registries

• Lists of disease events can be comprehensive in an area.
• They can help with tracking conditions or long term trends.
• Include: American Cancer Society, CDC, National Cancer Institute, American Association of Central Cancer Registries

Record Linkage

• Data from the population get merged from separate data sets.
• Info is merged by name or ID
• Can be used in clinical research to identify things like morbid conditions
• Every institute can maintain control or keep its information confidential

Health Indicators

• Important data for measuring the status of Canadians or healthcare systems
• Tools used by communities, governments or healthcare providers to monitor what is happening

Health Indicator Categories

• Health status
• Health system performance
• Community and health system characteristics
• Non-medical determinants of health
• Equity or disparity

Common Health Indicators

• Birth rate
• Fertility rate
• Causes of death
• Death rate (mortality)
• Infant/maternal mortality
• Years of potential life lost
• Life expectancy

Definitions of population, health, and disease

• Population: A group of people with some characteristic
• Includes age, sex, ethnicity, residence, or life event (retirement, etc)
• Ex: Residents, women giving birth or the homeless
• Health (WHO, 1948): A state of overall wellbeing, and no disease
• Disease (Last, 2001): Not at ease, with abnormal, or dysfunctional condition

Disease Measures

• Why measure disease?
• To have surveillance of outbreaks
• For prevention and planning purposes
• Need to quantify burden of disease
• To compare rates of disease
• To assess cost benefit Counts: Number of cases •Incidence: # of new cases in groups at risk •Prevalence: Total # of cases (new & old) during interval

Counts Examples

• There were 28 cases of lyme disease in Guelpherton
• 12 cases in Bryce-Muskimcoe
• Case definitions show evidence of disease
• Lyme Disease has a code
• PHAC compiles data
• Incidence per 100000 in Guelpherton is 55.3
• Incidence per 100000 Bryce is 96.6

Incidence

• Lyme Disease, for example, is measured this way.
• This number represents population at risk for disease, new cases over time
• Can be regarded as “average risk” in populations

Prevalence

• Measure of cases of disease over people at risk
• Point prevalence measured at time or interval
• The denominator excludes "population at risk."

Relationship between Incidence and Prevalence

• At the steady state, prevalence equals incidence over duration.
• Baseline prevalence is based on new and old cases.
• Manage cases to improve, not cure, rare diseases