Demographic Transition Model

Demographic Transition Model (or theory) is an approach that explains the changes populations undergo over time. This process generally refers to the shift from a traditional demographic regime characterized by high birth and high death rates to a modern demographic regime in which births are deliberately controlled and death rates have declined. This transformation is typically associated with a society’s transition from an agricultural society to an urban and industrialized one, and is characterized by a decline in death rates followed, with a lag, by a decline in birth rates.

Demographic Transition: The Transformation from Village to Urban Life (Generated by Artificial Intelligence)

Historical Development and Theoretical Approaches

Although the earliest observations of demographic change date back to the early 20th century, the foundations of the model were laid by Warren S. Thompson in his 1929 study. Thompson classified countries worldwide into three groups (Group A, B, C) based on their population growth rates and analyzed the differing trends in birth and death rates among these groups. However, Thompson did not present this classification as a theory.

The formulation of the demographic transition as a theory occurred in the United States after the Second World War, particularly in the context of high population growth rates in developing countries. During the second half of the 1940s, the theory was systematized through the work of the Office of Population Research at Princeton University, especially through the contributions of Frank W. Notestein (1945, 1953) and Kingsley Davis (1945, 1963). Notestein’s initial formulation stated that in traditional societies, high fertility was necessary to sustain population levels due to high mortality, and this condition was maintained by various social, religious, and cultural “props.” With the process of modernization—urbanization, industrialization, individualization, and the spread of education—death rates first declined, followed later by a weakening of these social supports and a rise in individual aspirations, leading to a decline in fertility rates.

Over time, criticisms and revisions of the theory emerged. For instance, it was argued that modernization, urbanization, and industrialization are not absolute prerequisites for demographic transition, as demographic change can occur without them. France’s decline in fertility in the late 18th century, before widespread industrialization or urbanization and without a marked drop in death rates, was cited as an example contradicting the theory’s initial assumptions. Similarly, research such as the Princeton European Fertility Project demonstrated that in some regions, fertility decline occurred before or simultaneously with the decline in mortality. This project also found that regions with similar levels of socioeconomic development but differing culturally—particularly linguistically—exhibited different fertility trends, while regions with different socioeconomic conditions but similar cultural traits showed similar trends. These findings highlighted the role of cultural factors and the diffusion of ideas in fertility change.

John C. Caldwell (1976), in an effort to reformulate the theory, challenged the notion that high fertility in traditional societies was “irrational,” arguing instead that behavior in both high- and low-fertility regimes is economically rational. According to Caldwell, the key determining factor is the direction of intergenerational wealth flow. In traditional societies, wealth flows from children to parents, making high fertility economically advantageous. With modernization, particularly under the influence of “Westernization”—through education and media promoting Western family structures and values—the family undergoes emotional and economic nucleation, reversing the direction of wealth flow from parents to children. After this “great divide,” low fertility becomes economically rational.

Additionally, approaches such as the “Second Demographic Transition Theory” have been developed to explain the decline of fertility below replacement levels and its persistence in advanced societies. This theory emphasizes the roles of individualization, secularization, rising non-marital births, and delayed marriage.

Stages of the Demographic Transition Process

The demographic transition model examines the process of population change by dividing it into distinct stages. While early formulations typically described three stages, later and more contemporary approaches have proposed four or even five stages. The five-stage model can be defined as follows:

Stage One (High Stationary)

In this stage, both birth and death rates are high. Death rates fluctuate due to epidemics, famines, and inadequate health conditions. Despite high birth rates, population growth is very slow or stagnant due to high mortality. Society is predominantly agricultural, with low levels of urbanization and education. The population structure is very young.

Stage Two (Early Expanding)

Death rates, particularly infant and child mortality, begin to decline rapidly due to improvements in health, hygiene, and nutrition. However, birth rates remain high. This results in a widening gap between birth and death rates, causing a sharp increase in population growth rate (a “population explosion”). The population structure remains young.

Stage Three (Late Expanding)

Birth rates begin to decline. Factors contributing to this decline include increasing urbanization, expanding education (especially for women), greater access to family planning methods, rising costs of childrearing, and reduced demand for agricultural labor. Death rates continue to decline but at a slower pace. Because the decline in birth rates outpaces the decline in death rates, population growth begins to slow, although the total population continues to increase.

Stage Four (Low Stationary)

Birth and death rates both reach low levels and stabilize. Population growth rate declines sharply, approaching zero or stabilizing. In this stage, even if the total fertility rate falls below the replacement level (approximately 2.1 children), population may continue to grow for some time due to “demographic momentum” or “population inertia,” caused by the large cohort born during earlier high-fertility periods entering reproductive age. The population structure begins to age.

Stage Five (Declining)

Birth rates fall below the already low death rates. This is primarily due to very low fertility levels combined with an aging population structure in which deaths outnumber births. This results in a decline in population size (negative population growth). This stage is observed in some developed countries, such as Japan, Germany, and several Eastern European nations.

Consequences of the Demographic Transition: Population Aging

One of the most prominent outcomes of the demographic transition process is population aging. Population aging refers to the decline in the proportion of children and young people within the total population, and the corresponding relative increase in the proportion of elderly people (typically aged 60 or 65 and over). This phenomenon results from declining fertility rates and increasing life expectancy in the later stages of the demographic transition.

Different studies use varying thresholds to define when a population is considered “aged.” Some studies indicate that a population is aged when those aged 65 and over constitute 8–10 percent of the total population, while others suggest the threshold should be 15 percent. More detailed classifications define populations with 10–19.9 percent elderly as “aged,” 20–29.9 percent as “very aged,” and 30 percent or more as “super-aged.”

Population aging produces various socio-economic consequences:

Labor Market

A decline in the proportion of the working-age population (typically aged 15–64) can lead to labor shortages. An increasing old-age dependency ratio (the ratio of elderly population to working-age population) raises the burden on the working segment.

Social Security Systems

Expenditures on pensions and old-age insurance rise. The shrinking working-age population and growing number of retirees place pressure on the financing of social security systems. In OECD countries, the share of pension expenditures in GDP has been observed to increase.

Health Expenditures

As the elderly population grows, the prevalence of chronic diseases and demand for health services increase, potentially driving up health expenditures. However, there are differing views on the magnitude of aging’s impact on health spending and the role of other factors such as technology and lifestyle.

Economic Growth

A reduction in labor supply and possible changes in savings rates may slow economic growth.

In response to these challenges, many countries—particularly those that have completed the demographic transition—have implemented various policies. The most prominent among these is raising the retirement age. While retirement ages vary across OECD countries, the general trend is toward increasing them. Some countries have indexed retirement age to increases in life expectancy. Countries such as Japan have introduced measures to encourage older people to remain in the labor force longer. Additionally, some countries have adopted pro-natalist policies aimed at increasing low fertility rates.

Demographic Transition in Türkiye

Türkiye is one of the countries undergoing the demographic transition. It began the transition later than European countries but has experienced it more rapidly. The stages of Türkiye’s demographic transition have been dated differently in various studies. According to the five-stage model, the classification is as follows:

Stage One (1923–1955)

The early years of the Republic were characterized by high but fluctuating death rates due to the effects of wars and high birth rates. Population growth rate declined during the Second World War years but remained generally positive. Infant mortality was very high and life expectancy low. Marriage age was low. The population structure was very young. During this period, pro-natalist policies were implemented to encourage population growth.

Stage Two (1955–1985)

Death rates, particularly infant mortality, began to decline rapidly due to improvements in health services. Although birth rates remained high, they started to decline from the 1960s onward. Population growth rate reached its highest level in Republican history during the early part of this period (1955–1960, around 2.85 percent) and then began to decline. Urbanization and rural-to-urban migration accelerated. From 1965 onward, policies aimed at slowing population growth (anti-natalist) were adopted. The average age of first marriage for women began to rise. The population structure remained young.

Stage Three (1985–2015)

The decline in birth rates accelerated. Total fertility rate approached or reached the replacement level (2.1 children) by the end of this period. Death rates continued to decline but at a slower pace. Population growth rate declined significantly. The total population continued to increase, but at a slower rate. The proportion of the young population (aged 0–14) decreased, while the proportion of the elderly population (aged 65+) began to rise.

Stage Four (2015–~2060):

Total fertility rate is at or below the replacement level. Population growth rate continues to decline. Due to demographic momentum, the population will continue to grow for some time, but at a very slow pace. The population is expected to peak around 2060 and then stabilize or begin to decline. Population aging becomes pronounced, with the elderly population share projected to exceed 15 percent in the 2040s.

Stage Five (~2060 and beyond):

According to population projections, birth rates are expected to fall below death rates, leading to a decline in population size. The population structure will age further.

Differences in the speed and timing of the demographic transition are observed across provinces and regions in Türkiye. Western regions entered the transition earlier and reached more advanced stages, while fertility rates remain higher in eastern and southeastern regions, and the transition is progressing more slowly. Population aging will remain a significant demographic and social policy issue for Türkiye in the future. The impact of the growing elderly population on social security and health systems, as well as rising pension expenditures, must be carefully addressed.