An Introduction to Aging and Demography Back »

Written by Bethany Stoutamire under the direction and review of Leacey E. Brown.


Why should we care about demography? Demography is the study of ourselves: where we live, how many children we have, and when we die. One tool is the Demographic Transition Theory, or the DTT. The DTT was developed by European demographers in the early 1900s to explain the fertility and mortality shifts that they were observing throughout Western Europe. In short, death rates and birth rates declined which led to the increase in the proportion of older people that we are seeing today. These demographers theorized that were four stages to the Demographic Transition Theory. This article will discuss these four stages to better provide a context for the discussion around population aging.

Phase 1

Phase 1 of the demographic transition theory was characterized by high fertility and high mortality. For most of human history, we were in phase 1 of the DTT as the population was around 10 million people. The world population began to expand in the early 1800s as advances in agriculture led to improvement in nutrition and lower infant mortality. This led to the second phase in the demographic transition

Phase 2

During phase 2, death rates began to fall and birth rates remained high, resulting in rapid population growth. Many countries that are classified as developing, such as Afghanistan, are considered to be in phase 2 of the demographic transition.

Phase 3

Phase 3 of the demographic transition theory is marked by lower death and declining fertility rates. The ability of a population to enter stage 3 of the DTT is often strongly tied to political and economic stability. Access to education and an increase in women’s status, are also other important factors, for as women become more educated, their fertility rates tend to decrease.

Phase 4

In Phase 4, both death and birth rates are low. The U.S., Canada, Argentina, China, and most of Europe are all examples of countries in this stage of the demographic transition theory.

Phase 5

How is there a fifth phase in a four phase theory? Phase 5 of the demographic transition theory is often contested, and would occur when fertility rates fall below death rates, which would result in a population that is declining, instead of growing or stabilizing. For the past several decades, Germany’s birth rate has been less than its death rate, however, the German population has continued to grow because of high rates of migration.

Why This Matters

Demographics help us anticipate what we might need for our communities. For example, the baby boom generation was the first large cohort of babies born in decades (prior to that the United States experienced the stock market crash, Great Depression and World War II which had a huge impact on birthrates). This large cohort of people moved through life they increased demand for various things (schools, entry level jobs, etc.). However, birthrates are lower now so the residents of our state may have different needs.

Time to Innovate

Adults older than 65 will soon out number child age 18 or younger in the United States. This is a historical first! This is an amazing opportunity for communities across our state. We have a huge pool of older people with knowledge and experience to help us address some of the most pressing concerns in our community (workforce shortages, outmigration, etc.).

Sources and Additional Readings:

  • What is the Demographic Transition Model?
  • Kinsella, K. and D.R. Phillips. 2005. “Global Aging: The Challenge of Success.” Population Bulletin, vol. 60. Washington, DC: Population Reference Bureau.
  • McFalls, J.A., Jr. 2007. “Population: A Lively Introduction, 5th Edition.” Population Bulletin, vol. 62 (1). Washington, DC: Population Reference Bureau.

Note: The above image is not necessarily an accurate representation of population growth and demography trends.

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