Introduction to Population Science

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, health beliefs of the public, public health, and patient safety and quality in the NHS to name just a few areas.

Here are some key definitions:

• Public Health - the branch of medicine aimed at; preventing disease, reducing health inequalities and improving health of the population through the organised efforts of society, often through governing bodies. In England, public health functions are led by bodies such as the UK Health Security Agency and the Office for Health Improvement and Disparities, whose roles include protecting and improving the nation’s health and reducing health inequalities.
• Population Science - a research based discipline that exists to have an impact on public health through its study of the things that can impact health incomes, and what can be done to improve those outcomes for the most people.
• Social Science - the study of human society and social relationships. This unit focuses specifically on relationships within the NHS, but lots of the ideas can be applied to a wider context.

Population Pyramids

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. It has two sides, male in blue and female in pink. This example has two horizontal lines, which indicate 15 and 65 years of age. This is done to separate the population into pre-working age, working age, and post-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. This means that there are a high number of children born per mother (causing a very wide bottom to the graph). However as child mortality is high, unfortunately many of these children do not reach adulthood. This is reflected in the severe narrowing above the younger ages as these children have died and as a result are not included in the older age bracket. This results in the characteristic pyramid with narrowing sides as seen 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 has 3.6 children, but their childhood mortality rate is not as high as Afghanistan, so 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 due to a lower average life expectancy and still substantial childhood mortality rate, the pyramid still narrows more severely than a stationary population. Furthermore, as older portions of the population were previously smaller as a result of these factors the top of the pyramid stays narrower until these portions die. This shape of pyramid is characteristic of many LEDCs (less economically developed countries).

An example of a stable population would be the USA. Despite the lowered fertility rates due to socioeconomic changes, there are a similar number of people being born to those who are dying. The average number of children per woman has been around 1.7 in recent years. As a result there is little difference in the size of younger and older populations leading to a more even pyramid characteristics 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 the improving healthcare, meaning that less babies are being born compared to people dying. The average number of children per woman is 1.4, and this is thought to be so low due to easy availability of contraception, increased education of women leading to women having children later in life, and the increased cost of having children in this country. As a result less 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 as a well developed study should reflect a cross section of a population. 

NB All data in the above section can be found here and are accurate to 2018 figures. 

Demographic transition model

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 are often described as moving through;

1. High deaths and high births. Life expectancy is low due to high infant mortality, poor sanitation, 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 is seen in the rapidly expanding pyramid.
2. 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.
3. Births begin to fall as deaths have plateaued. Too many children as a result are surviving past infancy leading to large unmanageable families. As a result, family planning and contraception become more widespread leading to a fall in births. Population however is still increasing as births still outstrip deaths even though they are falling.
4. Births and deaths are now both low again leading to a stable population but one that is older in its makeup. This is reflected in the stationary pyramid.

Some scholars discuss a fifth step, which is debated and may already be observable in some countries. There is debate over whether this will have further falls in births (the contracting pyramid) or will see an increase in births. This 5th stage is not universally accepted.

Economic transition model

This model discusses the transition of societies through the 3 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 3 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.

Domains of Public Health

There are three domains of public health:

• Health improvement - the effort to improve the health of the population. Some examples include: weight loss programs, smoking cessation services, treating pre-existing disease (like treating depression). This is important to maintain the health of the population, and for improving quality of life.
• Health protection - the effort taken to prevent disease developing in a population. Health protection is structured around; vaccination programmes, ensuring adequate sanitation, protecting against environmental hazards (eg. chemical spills), epidemic control and screening programmes (like cervical or bowel cancer). These can be expensive in the short term but can save the healthcare system money in the long run through reduction in disease burden.
• 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.

Types of Prevention

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 into 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 programs for breast and bowel cancer.
• Tertiary prevention is active treatment to prevent the negative consequences of an already established disease. This includes things like insulin therapy for Type II Diabetics and giving people with alcohol dependence thiamine supplementation to prevent complications such as Wernicke's encephalopathy.

Edited by: Dr. Thomas Burnell

Reviewed by: Dr. Marcus Judge

Quiz

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