Chapter 18

Population ChangesKey Terms

Domesday BookPronounced “doomsday” book, this was an outstanding medieval census conducted by William the Conqueror following his takeover of England in 1066.

CensusA population count, often recorded in terms of such categories as age, sex, occupation, marital status, and the like. The U.S. Census is conducted during the first year of each decade.

DemographyLiterally, written description of the people; the field of sociology devoted to the study of human populations with regard to how they grow, decline, or migrate.

Growth ratePopulation gains or losses computed by dividing the net gain or loss for a particular period by the population total at the start of that period.

Crude death rateThe total number of deaths for a year (or similar period) divided by the total population that year.

Crude birthrateThe total number of births for a year (or similar period) divided by the total population that year.

Fertility rate The total number of births for a year divided by the total number of women in their childbearing years (the U.S. Census bases this rate on all women age fifteen to forty-four).

Age-specific death ratesThe number of deaths per year of persons within a given age range divided by the total number of persons within that age range.

Birth cohortAll persons born within a given time period, usually one year.

Age structureThe proportions of persons of various age groups making up a total population.

Sex structureThe proportions of males and females in a population.

Expansive population structureAn age structure in which each younger cohort is larger than the one before it; such a population is growing.

Stationary population structureAn age structure in which younger birth cohorts are the same size as older ones were before mortality reduced them; such a population neither grows nor declines.

Constrictive population structureAn age structure in which younger cohorts are smaller than the ones before them; such a population is shrinking.

Arithmetic increase A constant rate of growth (or decline); the same number of units are added (or subtracted) each cycle, as in 1-2-3-4-5.

Exponential increaseA rate of growth (or decline) that speeds up as an increasingly larger number of units is added (or subtracted) each cycle, as in 1-2-4-8-16.

Positive checks According to Malthus, famine, disease, and war—the primary factors that check or stop population growth.

Malthusian theory of populationTheory stating that populations will always rise to, and then go somewhat above, the limits of subsistence and then will be reduced by the positive checks, only to rise again and be checked again.

Replacement-level fertility(sometimes called zero population growth) Point at which the number of births each year equals the number of deaths.

Demographic transitionA shift in population trends from high fertility, controlled by high mortality, to one of low mortality and low fertility.

Demographic transition theoryTheory stating that the demographic transition was caused by modernization, which reduced the need for and the value of large numbers of children.

Baby boomA brief period of high fertility in many Western industrial nations immediately following World War II.

Wanted fertilityThe number of children a couple wishes to have.