Readers question: Explain the main factors which affect population size and growth?
Population growth is determined by fertility rates (the number of children per adult) – fatality rates. Birth rates and mortality rates are, in turn, determined by a combination of factors. Often, economic growth and economic development have led to a decline in population growth, but there are no hard and fast rules and other factors, such as availability of family planning, social expectations and government intervention, can play an important role. But, we are seeing a big fall in fertility rates which is likely to cause a fall in populations quite soon.
Factors influencing population growth
- Economic development. Countries who are in the early stages of economic development tend to have higher rates of population growth. In agriculturally based societies, children are seen as potential income earners. From an early age, they can help with household tasks and collecting the harvest. Also, in societies without state pensions, parents often want more children to act as an insurance for their old age. It is expected children will look after parents in old age. Because child mortality rates are often higher, therefore there is a need to have more children to ensure the parents have sufficient children to look after them in old age.
- Education. In developed countries, education is usually compulsory until the age of 16. As education becomes compulsory, children are no longer economic assets – but economic costs. In the US, it is estimated a child can cost approx $230,000 by the time they leave college. Therefore, the cost of bringing up children provides an incentive to reduce family size.
- Quality of children. Gary Becker produced a paper in 1973 with H.Gregg Lewis which stated that parents choose the number of children based on a marginal cost and marginal benefit analysis. In developed countries with high rates of return from education, parents have an incentive to have a lower number of children and spend more on their education – to give their children not just standard education but a relatively better education than others. To be able to give children the best start in life, it necessitates smaller families. Becker noted rising real GDP per capita was generally consistent with smaller families.
- Welfare payments/State pensions. A generous state pension scheme means couples don’t need to have children to provide an effective retirement support when they are old. Family sizes in developing countries are higher because children are viewed as ‘insurance’ to look after them in old age. In modern societies, this is not necessary and birth rates fall as a result.
- Social and cultural factors. India and China (before one family policy) had strong social attachments to having large families. In the developed world, smaller families are the norm.
- Availability of family planning. Increased availability of contraception can enable women to limit family size closer to the desired level. In the developing world, the availability of contraception is more limited, and this can lead to unplanned pregnancies and more rapid population growth. In Africa in 2015, it was estimated that only 33% of women had access to contraception. Increasing rates would play a role in limiting population growth. (link)
- Female labour market participation. In developing economies, female education and social mobility are often lower. In societies where women gain a better education, there is a greater desire to put work over starting a family. In the developed world, women have often chosen to get married later and delay having children (or not at all) because they prefer to work and concentrate on their career.
- Death rates – Level of medical provision. Often, death rates are reduced before a slowdown in birth rates, causing a boom in the population size at a certain point in a country’s economic development. In the nineteenth and early twentieth centuries, there was a rapid improvement in medical treatments which helped to deal with many fatal diseases. Death rates fell and life expectancy increased.
Even since 1970, there has been significant growth in life expectancy
Back in 1900, the UK was the world’s richest economy, but its life expectancy was 47. The biggest difference was the percentage of children who died in infancy.
- Immigration levels. Some countries biggest drivers of population growth come from net migration. In the UK from 2000 to 2025, around 65% of net population growth came from net international migration. Countries like Japan with very strict immigration laws have seen a stagnation in the population.
- Historical factors/war. In the post-war period, western countries saw a ‘boom’ in population, as couples reunited at the end of the Second World War began having families. The ‘baby-boomer’ period indicates population growth can be influenced by historical events and a combination of factors which caused a delay in having children until the war ended.
The depressed economic conditions of 1929-39 caused a low birth rate. In the 10 years after the end of the Second World War, there was a spike in birth rates before falling to record low.
Population growth in the UK
Different UK population projections based on small changes in fertility rates and also different levels of migration.
Since 1992, the UK has experienced significant net migration which has been responsible for 60-65% of the UK’s population growth. (Gov.uk)
In the year to mid-2024, net international migration explained almost all the population rise in England and Wales (≈ 98% of population growth) (Guardian)
Fertility rates
In the UK fertility rates have fallen faster than predicted meaning that the UK has fewer births. At 1.4 the fertility rate is well below the replacement ratio of 2.1. This is a similar trend to the rest of the world.
Fertility rates have fallen across the world.
Only the Arab world and sub-saharan Africa have fertility rates above 2.1
The outcome is that Africa is forecast to gain a much bigger share of the global population.
One, caveat – it is quite likely that African birth rates will fall quicker than UN population forecasts from 2024.
Ageing population
The combination of higher life expectancy and falling birth rates means the composition of the population is changing with an ageing population.
The share of the US population over 65 will rise from 8% in 1960 to 22% by 2048.
Global Population
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