Chapter 2

Gross national income

Gross national income (GNI) is the total value of goods and services produced by the domestic economy of a country, within a given period of time, usually a year.

Closed population

In a closed population, there is no migration in or out of the population. The population's size and age structure are influenced only by fertility and mortality. No population, except the world as a whole, is completely closed. A closed population is often used in producing models.

Purchasing power parity (PPP)

PPP is an adjustment to a country's gross national income to account for differences among countries in the cost of living.

Population-balancing equation

PT2=PT1+B−D+I−O is the population-balancing equation, where all numbers refer to the country or region of interest, and where: PT2=Population at Time 2 PT1=Population at Time 1 B=Number of births between Time 1 and Time 2 D=Number of deaths between Time 1 and Time 2 I=Number of migrants into the country or region between Time 1 and Time 2 O=Number of migrants out of the country or region between Time 1 and Time 2 This equation shows all of the sources of population increase and population decline for a given geographic area between two dates.

Crude birth rate

The crude birth rate is the number of births to a population in a given year divided by the midyear population. The crude birth rate is typically expressed per 1,000 population. For example, a crude birth rate of ((4,000 births)/(population of 100,000))=.040 would be expressed as 40 per 1,000 population or just expressed as 40. More exactly, the crude birth rate is the number of births over a given period divided by the person-years lived by the population over that period.

Crude death rate

The crude death rate is the number of births to a population in a given year divided by the midyear population. The crude death rate is typically expressed per 1,000 population. For example, a crude death rate of ((2,000 deaths)/(population of 100,000))=.020 would be expressed as 20 per thousand population or just expressed as 20. More exactly, the crude death rate is the number of births over a given period divided by the person-years lived by the population over that period.

Population growth rate

The growth rate of a population is the number per 1,000 population by which a population grows in a year. If P1 is the population at the beginning of the year and P2 is the population at the end of the year, it can be calculated as 1,000×(P2−P1)/(midyear population). Since a population grows exponentially, it can be calculated as 1,000×(In(P2/P1).. It also can be calculated as (crude birth rate)−(crude death rate)+(in-migration rate)−(out-migration rate) which is the same as the rate of natural increase plus the net migration rate. If there are no migrants in or out of the population or if the number of in-migrants equals the number of out-migrants, the growth rate is equal to the rate of natural increase.

More developed region (MDR)

This is a UN classification. It comprises the countries of Europe, the United States, Canada, Japan, Australia, and New Zealand. The other countries are in the less developed region (LDR).

Less developed region (LDR)

This is a UN classification. It includes all of the countries except those in the more developed region (MDR).

Least developed countries (LeastDC)

This is a UN designation of countries defined by a combination of low income, human resource weakness, and economic vulnerability. Countries can move on and off this list.

Theory of the Demographic Transition

This is a descriptive model of the process by which the decline in death rates results in an increase in the rate of population growth, after which the growth rate declines once birth rates have declined. It was based on historical experience in Europe.

Net migration rate

This is actually the net in-migration rate. It is the number of migrants into an area in a time period minus the number of migrants out of the area in a time period, divided by the mid-period population of the area in thousands if the period of time is 1 year or divided by the person-years lived in the area in the time period in thousands.

Population pressure

This is the force exerted by a growing population upon its environment, resulting in dispersal or reduction of the population.

Carrying capacity

This is the maximum population size that the environment can sustain, given the food, habitat, water, and other necessities available in the environment.

Rate of natural increase

This is the number (typically, per 1,000 people) by which the population grows due to the excess of births over deaths. It is the crude birth rate minus the crude death rate.

Population doubling time

This is the number of years it would take for the size of the population to double if the population growth rate at a given point in time is positive and persisted indefinitely. The population doubling time can be calculated by dividing the population growth rate (expressed as a decimal, not per 1,000 population) into the natural logarithm of 2, which is 0.693. The population doubling time is a synthetic measure; it does not imply that the population will continue to grow at a given rate for any specific number of years. It provides a way to interpret the magnitude or the implications of different population growth rates.

Population halving time

This is the number of years that it would take for the size of the population to be reduced to one-half its size if the population growth rate at a given point in time is negative and persisted indefinitely. The population halving time can be calculated by dividing the population growth rate (expressed as a decimal, not per 1,000 population) into the natural logarithm of 2, which is 0.693. The population halving time is a synthetic measure; it does not imply that the population will continue to shrink at a given rate for any specific number of years. It provides a way to interpret the magnitude or the implications of different population growth rates.

Midyear population

This is the population of an area in the middle of the year. The midyear population, or an estimate of the midyear population, is often used as the denominator for rates, such as the crude birth rate or the crude death rate.

Theory of Demographic Change and Response

This is the view that when there is population increase due to mortality decline, people have a variety of options as to how to respond in addition to voluntary fertility limitation. Some of the other options include migration, abortion, and infanticide.