The Theory of Demographic Transition

The Theory of Demographic Transition

This theory links population growth directly to a society’s level of economic development. It argues that every society moves through a predictable pattern of population change as it develops. The core idea is that population growth is not random — it follows the stages of economic progress.

The theory identifies three basic stages of population growth.

Stage 1: Low population growth in an underdeveloped, technologically backward society.

Both the birth rate and the death rate are very high. Because they are both high, the difference between them — the net growth rate — is small. Growth is low, but for the wrong reasons: high death rates cancel out high birth rates. This stage is typical of pre-industrial, poor societies.

Stage 2: The transitional stage — a period of very high population growth.

This is the stage of the ‘population explosion’. It occurs when a society begins to develop economically. Death rates fall quickly, thanks to better disease control, improved public health, and better nutrition. But birth rates do not fall as fast. Why? Because reproductive behaviour is slow to change. People’s family-size decisions were shaped during times of poverty and high child mortality, when having many children was a survival strategy. It takes time for society to adjust to new conditions of relative prosperity and longer life spans. The gap between a low death rate and a still-high birth rate produces very rapid population growth.

Stage 3: Low population growth in a developed society.

Both the birth rate and the death rate have been brought down to low levels. The difference between them is again small, so population growth is low. This is the stage of a mature, industrialised economy.

This pattern was first observed in Western Europe during the late nineteenth and early twentieth centuries. Today, less developed countries are trying to follow a similar path — struggling to reduce their birth rates to match their already-lowered death rates. In India, the demographic transition is not yet complete: the mortality rate has fallen significantly, but the birth rate has not come down to the same extent.

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Common Concepts and Indicators

Most demographic concepts are expressed as rates or ratios. Each rate compares two numbers: the specific statistic for a geographical area (a country, state, district, etc.) and a standard for comparison (usually per 1000 population).

Birth rate — the number of live births in a given area during a given year, divided by the total population of that area, expressed per 1000 people.

Death rate — the number of deaths in a given area during a given year, per 1000 people.

Both rates depend on families reporting births and deaths accurately.

Rate of natural increase (growth rate) — the difference between the birth rate and the death rate. When this difference is zero (or very small), the population is said to have ‘stabilised’ or reached the ‘replacement level’. This is the rate of growth needed for new generations to replace the older ones that are dying out.

Fertility rate — the number of live births per 1000 women in the child-bearing age group (usually taken as 15 to 49 years). Like the birth and death rates, this is a ‘crude’ rate — it is a rough average for the entire population and does not account for differences across age groups. Demographers also calculate age-specific rates to get more precise information.

Infant mortality rate — the number of deaths of babies before the age of one year, per 1000 live births.

Maternal mortality rate — the number of women who die in childbirth, per 1,00,000 live births.

High infant and maternal mortality rates are clear indicators of backwardness and poverty. Development brings sharp falls in these rates as medical facilities, education, awareness, and prosperity increase.

Life expectancy — the estimated number of years an average person is expected to survive. It is calculated using data on age-specific death rates in a given area over a period of time.

Sex ratio — the number of females per 1000 males in a given area at a specified time.

Historically, most countries have slightly more females than males. This is surprising because slightly more male babies are born than female ones — nature produces roughly 943 to 952 female babies for every 1000 males. Yet the sex ratio is often in favour of females for two reasons:

• Girl babies have a biological advantage in resisting disease during infancy.
• Women tend to outlive men in most societies, so there are more older women than men.

Together, these factors produce a sex ratio of roughly 1050 females per 1000 males in most contexts. However, the sex ratio has been declining in some countries — notably China, South Korea, and especially India. This decline is linked to social norms that value males much more than females, leading to ‘son preference’ and the relative neglect of girl babies.

Age structure — the proportion of persons in different age groups relative to the total population. The age structure changes with development and life expectancy. …