Population Growth and the Demographic Transition Ian RH Rockett, PhD, MPH Professor and Associate Chair Department of Community Medicine West Virginia University PO Box 9190 Morgantown, WV USA

Learning Objectives 1.To view population growth from a Malthusian perspective 2.To calculate crude death rates, birth rates, rates of natural increase, and population doubling times 3.To comprehend the concept of the Demographic Transition

Performance Objectives 1.Examine patterns of natural increase 2.Classify populations and sub- populations within the demographic transition framework 3.Predict growth trends in populations and sub-populations

Demography a kindred population science with epidemiology, it shares the Greek root demos (people) and the same founder, 17 th century Englishman, John Graunt

Demography is the scientific study of the determinants and consequences of human population trends

By the beginning of the 21 st century, world population reached 6 billion. Most of the growth has occurred in the past 200 years.

Figure 1 World Population Growth Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 38Population: A Lively IntroductionPopulation Reference Bureau

The unprecedented population growth of modern times heightens interest in the notion of doubling time. Calculation of population doubling time is facilitated by the Law of 70.

Law of 70 If a population is growing at a constant rate of 1% per year, it can be expected to double approximately every 70 years -- if the rate of growth is 2%, then the expected doubling time is 70/2 or 35 years.

T.R. Malthus, English clergyman, Thomas Robert Malthus, was the first person to draw widespread attention to the two components of natural increase, births and deaths (fertility and mortality).Malthus

In his Essay on the Principle of Population, initially published in 1798, Malthus postulated that population tended to grow geometrically while the means of subsistence (food) grew only arithmetically.Essay on the Principle of Population

The Malthusian Trap arithmetic growth (food): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10… geometric growth (population): 1, 2, 4, 8, 16, 32, 64, 128, 256, 512…

Malthus argued that the difference between geometric and arithmetic growth caused a tension between the growth of population and that of the means of subsistence. -- this gap could not persist indefinitely.

Owing to war, disease, hunger, and vice, mortality would serve as a positive check on population growth.

Solution to the Malthusian Trap Preventive checks: birth control through (1) later age at marriage. (2) abstinence from sex outside marriage. (Malthus opposed artificial methods of birth control on moral grounds. Viewed contraception as a vice)

Population Explosion Contrary to Malthuss prediction, mortality has not yet risen to curb world population growth. < 1 billion people in billion by the end of the 20 th century

Population Explosion Why was Malthus unable to foresee the population explosion (also known as the population bomb)?population bomb He did not recognize the force of the Industrial Revolution, which produced exponential growth in the means of subsistence.

The Demographic Transition During the first half of the 20 th century, demographers conceived the notion of the demographic transition.

The Demographic Transition The demographic transition framework illustrates population growth in terms of discrepancies and changes in two crude vital rates – mortality and fertility (ignores migration)

CRUDE VITAL RATES Crude Death Rate (CDR) = # deaths in calendar year * k mid–year population

CRUDE VITAL RATES Crude Birth Rate (CBR) = # deaths in calendar year * k mid–year population Rate of Natural Increase = CBR - CDR

Figure 2 The Demographic Transition Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 39Population: A Lively IntroductionPopulation Reference Bureau

Four Perspectives on Demographic Transition

(1)Description (2) Classification

(3) Explanation (4) Prediction

Figure 3 Demographic/ Epidemiologic Transition FrameworkEpidemiologic Transition Source: Ian R.H. Rockett. Population and Health: An Introduction to Epidemiology. Second edition. Population Reference Bureau 54(4); 1999: 9Population Reference Bureau