The demographic transition model (DTM) is a model that explains the changes in population over a period (Bongaarts, 2009). Warren Thomson, an American demographer, developed the model, when he made the demographic interpretations of industrialized countries in 1929. Beginning 1700s owing to developments in the technology and improvements in the agriculture sector, the population changes occurred. Many people lived beyond their adolescents, life expectancy increased with reduction in death rates and increasing birth rates. Demographers noted the differences on population demographics, which were initially the same regardless of geographic location. Consequently, demographers developed the demographic transition model to explain these population changes. The demographic transition model is based on the population trends of two demographic characteristics; the death and birth rates.
The Phases of the Demographic Transition Model (DTM)
The birth and death rates in the demographic transition model were used to represent the growth cycles of populations through various stages as a country transitions in economic development (Bongaarts, 2009). These cycles of population changes are represented in four stages; stages1, 2, 3 & 4.
This is the initial stage in the DTM, which represents the developments before the era of the industrial revolution. In this stage, the birth and death rates are constant and population sizes are virtually constant. The only factors that could alter the population sizes at this stage are the spread of pandemics or wars. The number of births in a thousand (crude birth rate) and the number of deaths in a thousand (crude death rates) are constant.
The second stage is characterized by high birth rates and lower deaths rates. The introduction of medicine helps in lowering the death rates, while the birth rates remain high. This stage characterizes the least developed countries of the world, for example, African and Asian countries. At this stage, owing to improved healthcare due to presence of vaccines and other medicines, the crude death rates are lower. Therefore, the population growth rate remains high due to high crude birth rate and lower crude death rates.
The third stage of the DTM is characterized by a steady decline in death and birth rates. The decrease in the crude birth rates at this stage is attributed to increased use of contraception, improved economic conditions and the women gaining more status in the society. Although the population grows, the rate of growth at this stage is slow, compared to that in stage two.
This is the final phase of the demographic transition model and is characterized by a stable population with low crude birth and crude death rates. The stage is evident in the developed countries, which have better healthcare, a higher proportion of women in the job market and better education. The fertility rate in the countries within this stage is around two children per couple.
According to the demographers, the second stage of the DTM has lower CDR owing to improved healthcare, increased economic growth and sufficient food production (Bongaarts, 2009). In addition, the decline in crude birth rates in the third stage owes to the lower infant mortality rates, increased materialism where families prefer to spend more on items compared to many kids, changes in fashions and social trends and preference for smaller families.