4. The entrance of statistics and mathematical models

By the 19th century the study of demography had developed from John Graunt’s primitive life table to the complex statistical laws and theories of Benjamin Gompertz and William Makeham. ‘The entrance of statistics and mathematical models’ describes the Gompertz–Makeham law of mortality, the first parametric model of human mortality that is still valid today, and the formation of the International Union for the Scientific Investigation of Population Problems in 1927. It also outlines the contributions of William Farr, Francis Galton, Karl Pearson, Sir Ronald Aylmer Fisher, Leonard Henry Tippett, Ansley Johnson Coale, William Brass, and John ‘Jack’ Caldwell to the development of demography and demographic methods and analysis from the 19th century to the 21st century.

8. Population pyramids and projections

‘Population pyramids and projections’ describes a key concept within demography—the population pyramid. The age pyramid represents the distribution of a population by age and sex. It comprises a pair of bar graphs joined in the centre and traditionally resembling an Egyptian pyramid. The vertical axis records age, with young at the base and old at the top, and the bars coming off the axis to the right represent females and to the left males. The demographic behaviour of individuals is affected by their age, the time period in which they are living, and their shared cohort experience. Different methods of population projections to foresee population futures are also outlined.

1. Demography is destiny … or not

It is increasingly recognized that population change plays a key role in our political systems, economies, and societies at the local, national, regional, and global level. ‘Demography is destiny … or not’ explains that demography has at its core the notion of drivers of population change—mortality, fertility, and migration—and how these then interact to change populations. Contemporary demography is divided into three separate areas of study: the characteristics of past or current populations, with regard to their size and make-up; the different demographic drivers that directly influence this composition, primarily fertility, mortality, and migration; and the relationship between these static characteristics and dynamic processes and the social, economic, and cultural environments within which they interact.

7. A demographer’s toolbox

‘A demographer’s toolbox’ looks at the tools, models, methods, assumptions, and uncertainties within the practice of demography. Demographers need to know that they are really finding out the things they want to know and that their methods and sources of data are robust and are accurately answering their questions. There are four main sources of demographic data: census, registration records, surveys, and ethnographic material. The 1980s and 1990s saw an increasingly sophisticated adoption of mathematical models, needed to cope with the growing availability of demographic data. The arrival of modern computing methods also transformed the power of demographic analysis. Recently, probability, competing risks, hazard functions, and bio-markers have been added to the demographer’s toolbox.

5. The drivers

The size, growth, density, distribution, and age structure or composition of a population is broadly dependent on three drivers: fertility (numbers of births), mortality (number of deaths), and migration (number of moves in and out of that population). ‘The drivers’ explores the ideas behind our understanding of these drivers on which most demographic analysis is focused. It explains that the main measures of fertility in a population are the Crude Birth Rate and the Total Fertility Rate. The main measures of mortality are the Crude Death Rate and life expectancy. Migration is different in that while mortality and fertility are typically studied within a closed population, migration introduces the notion of an open population.

9. Sub-disciplines arise

While most of the social science disciplines deal with people, some have developed a specific interest in demographic analysis and demographic theories, and these have been formalized into sub-disciplines of demography. In many cases they represent a merging of an area within the main discipline of demography. ‘Sub-disciplines arise’ looks at several of these sub-disciplines in turn: anthropological demography, bio-demography, economic demography (or population economics), family demography, historical demography, mathematical demography, palaeodemography, population geography (or spatial demography), population studies, and social demography. These all now form part of a broad field of population studies that analyse the relationships between economic, social, cultural, and biological processes influencing a population.

3. The fathers of demographic thought

Demographic ideas can be traced back to antiquity, but it is generally accepted that demography originated in the middle of the 17th century with the English statistician, John Graunt (1620–74), and his primitive life tables, which were the first attempt to examine statistical regularities inherent within the numbers of births and deaths. ‘The fathers of demographic thought’ describes the diverse theorists who founded and developed the study of demography. It begins with Graunt and then outlines the input of Sir William Petty (1623–87), Edmund Halley (1656–1742), Richard Price (1723–91), and Thomas Malthus (1766–1834). Their foundations were central to developing the relationship between analytical reasoning, numerical problems, and arithmetical records.

2. From 55,000 to 7 billion

‘From 55,000 to 7 billion’ describes how global population has evolved over time and space, experiencing a small increase for thousands of years, until around 200 years ago when global population grew dramatically. 1.2 million years ago there were around 55,000 humans, then by the end of the last ice age 20,000 years ago there were around 1 million Homo sapiens. The next 15,000 years saw a dramatic evolution in human economy and society and by 5000 bc the world population reached around 5 million. It took a further 7,000 years for population to reach one billion by ad 1800. Population now stands at some 7 billion and is projected to reach around 10 billion during this century.

10. Population policies and future challenges

Population policies aim to modify the growth rate, composition, or distribution of a population. In practice, they can be explicit or implicit. The two main areas in which governments attempt to control or influence through population polices are fertility and migration. ‘Population policies and future challenges’ also considers some key population challenges of the 21st century. Will fertility rates fall to replacement in sub-Saharan Africa? What is the relationship between environment, population, and consumption in different parts of the world? How will we feed and provide water for the projected 9 or 10 billion of us by 2050? What will be the impact of the ageing of the world’s population and of technological change?

6. The demographic transition—centrepiece of demography

The demographic transition is regarded as a centrepiece of demography. It is the series of changes that occur as countries evolve from a stable state of high mortality and high fertility to one of low mortality and low fertility, but its timing and drivers are strongly debated. ‘The demographic transition—centrepiece of demography’ explains that demographic transition theory can be divided into three broad components: first, the changes over time in mortality and fertility, based on clear data and therefore generally uncontested; second, and the most controversial, the construction of causal models to explain the timing, pace, and drivers of these changes; and third, the attempt to predict future changes especially for countries of the South.