Demographic Transition Model

The demographic transition model, which is attributed to demographer Frank Notestein, describes population changes in fertility and mortality as societies make the transition from premodern to postmodern eras. In essence, the premodern regime of high rates of births and deaths changes to low rates of each through the process of modernization.

Much has been written about this topic regarding the pace, pattern, and causes of this transition. This entry first describes the basic demographic transition model and describes some of the different ways countries have moved through the transition. The next section describes the epidemiologic transition theory, which focuses primarily on mortality transitions. The third section examines the effect of the demographic and epidemiologic transition on population size and structure. Discussion then focuses on the possible causes for the mortality and fertility declines. The final section considers current and future trends in demographic and epidemiologic transitions.

Basic Demographic Transition Model

The basic demographic transition model is depicted in Figure 1. During the premodern times (Stage One) both fertility and mortality rates are high and fluctuating. In the second stage mortality rates begin to decline while fertility rates remain high. Stage Three is marked with declines in both mortality and fertility, and in the last stage both mortality and fertility rates are low.

Figure 1 Demographic Transition Model

The demographic transition model was initially based on changes that occurred in Western European societies. For most countries large and irreversible declines in death rates occurred first, followed by declines in birth rates. No two countries have followed the same transition due to varied differences in patterns of marriage, fertility, and mortality, as well as differing cultural norms and values, at each stage. In Western Europe the mortality decline lasted from the latter part of the 18th century through the first half of the 19th century, whereas in less developed countries it began in the 20th century. The duration of the transition has also varied widely. The transition in Western Europe occurred over 75 to 100 years; in Eastern Europe, 20 to 25 years; and an even shorter period for those countries moving through the transition in the 20th century. In non-Western nations a decline in mortality has always preceded the decline in fertility. Indeed all countries that have gone through modernization have also experienced the demographic transition, and it has occurred under vastly different socioeconomic conditions.

Epidemiologic Transition Theory

The epidemic transition theory focuses on changes in the complex patterns of disease and mortality. Omran, the author of this theory, believed that demographic transition models overemphasized the role of fertility in population dynamics. His rationale was that in premodern societies the range of natural fertility is limited, based on the survival of women to reproductive ages, marriage patterns, and contraceptive practices, whereas the death rate could have no upper limit.

The focus of the epidemiologic transition is on shifts in disease patterns and causes of death, and the resultant impacts on life expectation. There are three basic stages in the epidemiologic transition: (1) the age of pestilence and famine, (2) the age of receding pandemics, and (3) the age of degenerative and “man-made” diseases.

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