By Dr. Maddie Swannack and Dr. Ben Appleby
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Core
Aims of the Population and Social Science unit
This unit is a compilation of many different focuses that can all fit under the heading of ‘Population and Social Science’. It includes articles on epidemiological study designs, how to interpret the data from studies, and health beliefs of the public. It also covers public health, and patient safety and quality in the NHS, to name just a few areas.
Here are some key definitions:
- Public Health - the science and art of preventing disease, prolonging life and promoting health through the organised efforts of society. It also aims at reducing health inequalities (unfair and avoidable differences in health between groups of people). In England, each local authority must take such steps as it considers appropriate to improve the health of the people in its area. At national level, the UK Health Security Agency (UKHSA) protects people from health threats such as infectious diseases, chemicals and radiation. The Office for Health Improvement and Disparities (OHID), which is part of the Department of Health and Social Care, works to improve the nation’s health and reduce health disparities.
- Population Science - a research-based discipline that exists to have an impact on public health. It studies the things that can affect health outcomes, and what can be done to improve those outcomes for the most people.
- Social Science - the study of human society and social relationships. The social science articles in this unit focus on relationships within the NHS, but lots of the ideas can be applied to a wider context.
Population pyramids are useful tools which help visualise the shape of populations. Population pyramids display percentage of the population on the x-axis against age on the y-axis. A pyramid has two sides: male in blue and female in pink. The diagram below has two horizontal lines, which indicate 15 and 65 years of age. The lines separate the population into pre-working age, working age and post-working age. These are the usual international cut-offs: the World Bank counts ages 15 to 64 as working age.
Diagram: Shows four common shapes of population graph, plotting age on the y axis against percentage of population at that age on the x axis. It has two halves, with female population in pink, and male population in blue.
SimpleMed original by Dr. Maddie Swannack
Population pyramids can be useful in displaying multiple features of a population. One key feature is change in population size.
An example of a rapidly expanding country would be Afghanistan. Afghanistan has a very high fertility rate (the average number of children born per woman): 5.3 in 2018 and 4.8 in 2024. This means that there are a high number of children born per mother (causing a very wide bottom to the graph). Child mortality is also high: in 2018, 64.8 of every 1,000 children born alive died before their fifth birthday (about 1 in 15). Births far outnumber deaths, so the population is growing and each age group is larger than the one above it. Deaths in childhood and in later life also mean that fewer people survive into the older age groups. Together these cause the severe narrowing above the youngest ages. This results in the characteristic pyramid with narrowing sides, as in the rapidly expanding pyramid in the diagram above. This shape of pyramid is characteristic of many LDCs (least developed countries).
An example of an expanding population would be Iraq. This is because the average woman had 3.5 children in 2018 (3.2 in 2024). However, the childhood mortality rate is not as high as in Afghanistan: 26.5 deaths per 1,000 live births before the age of five in 2018, compared with 64.8. More of those children live into adulthood, resulting in a less severe narrowing and a more ‘pyramid’ shaped pyramid. It is important to note that life expectancy (the average number of years a person is expected to live) and child survival are still lower than in the USA or Japan. In Iraq, life expectancy was 71 years in 2018. As a result, the pyramid still narrows more severely than a stationary population (also called a stable population: one whose size stays roughly the same). Furthermore, the older age groups are smaller, because fewer babies were born in earlier decades and more people died young. The top of the pyramid stays narrower until the larger younger groups grow old. This shape of pyramid is characteristic of many LEDCs (less economically developed countries).
An example of a stationary population (one whose size changes only slowly) would be the USA. Fertility rates have lowered due to socioeconomic changes, and the average number of children per woman was 1.7 in 2018 (1.6 in 2024). Births (11.6 per 1,000 people in 2018) only moderately outnumber deaths (8.7 per 1,000), so the population changes size slowly. As a result there is little difference in the size of younger and older populations. This gives a more even pyramid, which is characteristic of an MEDC (more economically developed country).
An example of a contracting population would be Japan. This stems from the decreasing fertility in this country (and across much of the developed world) and from long lifespans (life expectancy was 84.2 years in 2018). This means that fewer babies are being born than people dying: there were 7.4 births and 11.0 deaths per 1,000 people in 2018. The average number of children per woman was 1.4 in 2018 and had fallen to 1.15 by 2024. The fertility rate in Japan is thought to be so low because of fewer marriages, women having children later in life as their education increases, and the increased cost of having children. As a result fewer children are being born, leading to a narrower bottom, and with longer lifespans the top of the pyramid is staying wide.
It is important to understand the shape of the population that is going to be studied. This is because a well developed study should reflect a cross section (a representative mix) of a population.
Note that all data in the above section can be found here (World Bank). Figures are for 2018 unless a year is given. The World Bank groups countries by income, and currently classes Afghanistan as low income, Iraq as upper middle income, and the USA and Japan as high income.
The demographic transition model shows the change in population numbers over time and can be related to population pyramids. The model describes four stages that societies often move through:
- High deaths and high births. Life expectancy is low due to high infant mortality, poor sanitation (a lack of clean water and safe sewage disposal), famine and disease. However, the population is stable due to high birth rates to compensate and there is little family planning or use of contraceptives. As a result there is a relatively constant population of younger individuals. This gives a wide base that narrows steeply, as in the rapidly expanding pyramid, even though the population itself is not growing quickly at this stage.
- Deaths begin to fall where births are still high. Life expectancy begins to improve through improvements to the above factors as the society industrialises and develops. However, births are still high. As a result the total population grows dramatically. This is reflected in the expanding pyramid.
- Births begin to fall while deaths are already low. Family planning and contraception become more widespread as societies develop, leading to a fall in births. Population however is still increasing as births still outstrip deaths, even though births are falling.
- Births and deaths are now both low, leading to a stationary population (one whose size stays roughly the same) but one that is older in its makeup. This is reflected in the stationary pyramid.
Some scholars propose a fifth stage, which may already be observable in some countries. In it, births could fall further (the contracting pyramid) or rise again. This fifth stage is not universally accepted.
This model discusses the transition of societies through the three sectors of an economy. The model suggests that societies often develop by moving through the three sectors, although in practice these stages may overlap.
The three economic sectors are:
Primary sector - resource production and extraction - e.g. mining, agriculture and fishing.
Secondary sector - manufacture of products.
Tertiary sector - services e.g. banking, accountancy, finance, medicine.
There are three domains of public health:
- Health improvement - the effort to improve the health of the population. Some examples include: weight loss programmes, smoking cessation (stopping smoking) services, and tackling the wider causes of ill health, such as poor housing and unemployment. This is important to maintain the health of the population, and for improving quality of life.
- Health protection - the effort taken to protect the population from infectious diseases and environmental hazards. Health protection includes vaccination programmes, ensuring adequate sanitation, protecting against environmental hazards (e.g. chemical spills) and epidemic control. It also includes screening programmes for infectious disease, such as screening in pregnancy for hepatitis B, HIV and syphilis (a bacterial sexually transmitted infection). These measures can be expensive in the short term but can save the healthcare system money in the long run through reduction in disease burden (the amount of illness in a population).
- Healthcare Public Health - this is the provision of healthcare and studies to improve healthcare itself. This involves: provision and prioritisation of services, funding decisions and researching improvements in healthcare.
There are three types of prevention that can be applied in healthcare.
- Primary prevention is the process of trying to prevent a disease from occurring in the first place. This includes interventions like immunisations, taxes on cigarettes and alcohol, public health campaigns about weight loss or smoking cessation, and the use of fluoride toothpaste.
- Secondary prevention is the process of detecting disease in its early stages, before it becomes serious. This includes things like screening programmes for breast and bowel cancer.
- Tertiary prevention is active treatment to prevent the negative consequences of an already established disease. This includes things like treatment to control blood glucose and protect the heart and kidneys in people with type 2 diabetes. Medicines taken by mouth, such as metformin, are usually used first, and insulin is used later in some people. It also includes giving thiamine (vitamin B1) supplements to people who are dependent on alcohol and at high risk, such as those who are malnourished or in alcohol withdrawal. The aim is to prevent complications such as Wernicke’s encephalopathy (a brain disorder caused by thiamine deficiency).
Edited by: Dr. Thomas Burnell
Reviewed by: Dr. Marcus Judge
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