Principles of Demography

Demography Defined
- Demography is the study of statistics related to the composition of human populations.
- Demographers analyze population data using statistical tools.
- A population refers to all people living in a specific geographic area.
- Demographics summarize census data for various purposes such as government planning.
- Demographic analysis helps identify cultural, political, and economic factors contributing to social problems.

Crude Birth Rate (CBR)
- CBR refers to the number of births in a defined population during a given year, typically expressed as births per 1,000 women per year.
- CBR can be affected by various factors including historical events (e.g., post-World War II baby boom).
- Period Effects affect CBR, which are changes that impact all age groups at a particular time.
Replacement Fertility
- This is the fertility level required to replace members of a population, which is about 2.1 live births in developed countries.
- In regions with high mortality rates (e.g., sub-Saharan Africa), the replacement rate is higher (approx. 2.7).
- It is also defined as the number of live births per woman over her fertile period.

Mortality Rate
- Measures the frequency of death in a population during a specified time.
- Crude Death Rate (CDR) is calculated as total deaths divided by the midyear population, expressed as deaths per 1,000.
- Age-Specific Death Rate shows mortality rate by specific age groups (e.g., infants, young adults).
Population Pyramids
- These graphs represent the age-sex distribution of a population and can indicate the sex ratio and historical fertility/mortality rates.
- Weighting average death rates is often equal to the crude death rate.
Infant Mortality Rate
- This percentage reflects infants who die before their first birthday per 1,000 live births annually, indicating overall health status.

Life Span
- Maximum age attainable under optimal conditions, estimated biological limit is about 120 years.
Life Expectancy
- Average number of years a person can expect to live, influenced by factors like health care, nutrition, and sanitation.
Population Growth
- Refers to an increase in the number of people in a defined area over time, driven by natural increase (births - deaths) and net migration.
- Immigration is the moving of foreign populations into a country, while emigration is the opposite.
- Net Migration is the difference between immigration and emigration.

Population Density
- Number of people per square mile (or square kilometer).
Dependency Ratio
- Measures the number of dependents (ages 0-14 and 65+) to those economically productive (ages 15-64).
Overpopulation vs. Underpopulation
- Overpopulation occurs when resources are insufficient; underpopulation occurs when there are too few people to utilize resources effectively.
Population Composition
- Characteristics of a population, including age and gender.
Population Distribution
- Describes the geographical location of a population, influenced by climate, topography, resources, and economic/political realities.

Historical population growth has shown significant increases primarily since 2000 BCE.
Current global population trends illustrate ongoing growth despite decreasing growth rates.
Natural Increase = CBR - CDR; notable changes in global growth rates recorded from the CIA World Factbook:
- Global birthrate (2009): 1.86%, mortality rate: 0.78%, growth rate: 1.08%.
Demographic Transition Theory:
- Stages reflect transitions from high to low birth and death rates due to industrialization:
1. Stage 1: High birth/death rates, preindustrial.
2. Stage 2: Declining death rates, high birth rates (e.g., countries in sub-Saharan Africa).
3. Stage 3: Low death rates, declining birth rates (e.g., Mexico, South Africa).
4. Stage 4: Low birth/death rates, stable population (e.g., United States, Japan).
5. Stage 5: Birth rates drop below replacement levels; death rates exceed birth rates (e.g., Germany, Japan).