Demographic transition refers to the process of change in a population's demographic structure over time. It involves a shift from high birth and death rates to low birth and death rates, accompanied by changes in population growth rates, age distribution, and overall population size. The transition is typically observed as a society undergoes economic and social development.

The demographic transition theory, proposed by Warren Thompson in 1929, outlines four distinct stages through which countries progress as they experience demographic changes. These stages provide a framework for understanding the patterns of population growth and the associated social and economic implications.

The Four Stages of Demographic Transition:

Stage 1: High Stationary
- This stage reflects the historical pattern of pre-industrial societies.
- Birth and death rates are both high, resulting in a relatively stable population size.
- Limited access to healthcare, high infant mortality, and low life expectancy are characteristic of this stage.
- Population growth is slow, if any.

Stage 2: Early Expanding
- This stage marks the beginning of industrialization and improved living conditions.
- Death rates decline due to advancements in healthcare, sanitation, and access to clean water.
- Birth rates remain high, leading to a significant increase in population size.
- The population growth rate accelerates, resulting in a rapid population expansion.
- The age structure becomes younger, with a larger proportion of the population in younger age groups.

Stage 3: Late Expanding
- This stage is characterized by further improvements in healthcare, education, and economic development.
- Birth rates start to decline as a result of changing social norms, increased access to contraception, and urbanization.
- Death rates continue to decrease or stabilize at a low level.
- Population growth rate gradually slows down, but the overall population size continues to increase.
- The age structure begins to shift, with a growing proportion of the population entering adulthood and middle age.

Stage 4: Low Stationary
- In this stage, both birth and death rates are low, leading to a stable population size.
- Birth rates may even drop below replacement level, resulting in population decline over time.
- Population growth rate approaches zero or becomes negative.
- The age structure becomes older, with a significant proportion of the population in older age groups.
- This stage is often associated with developed countries that have achieved high levels of economic and social development.

Implications and Significance:
Understanding the stages of demographic transition is essential for policymakers and planners, as it helps anticipate future population trends and their potential impact on various sectors, such as healthcare, education, and labor force. It can guide the formulation of policies related to family planning, healthcare infrastructure, and social security systems. Additionally, the demographic transition theory emphasizes the importance of investing in education, women's empowerment, and economic development to facilitate the transition to lower birth and death rates. Ultimately, achieving a stable and balanced population growth can contribute to sustainable development and improved quality of life.