Structure of the population pyramid
The population pyramid consists of several key elements. In its traditional, most commonly used form, the population pyramid depicts the frequencies or percentages for the age variable in a given sample or population, broken down by the gender variable (Figure 1).
Figure 1. Population pyramid showing the distribution of age by gender in the studied group of adults.
Although this form of population pyramid is most commonly encountered, this chart can also be used if you only have qualitative variables - then the variable whose distribution is being analyzed will be presented in the form of a bar chart, instead of a histogram.
Still another form is the use of a population pyramid broken down into more categories. In such a case, the graph is divided into respective multiple axes against which the data are presented. In this form, comparing histograms or bar charts in pairs is just as easy, but if you want to compare two groups that are not adjacent to each other on the visualization, this form is unfortunately already less clear (Figure 2).
Figure 2. Population pyramid showing age of respondents by 6 household categories.
Interpreting the population pyramid
The population pyramid can take a variety of shapes that reflect characteristic changes in the structure of society over the years[1]. Here we will focus only on the basic interpretation of the chart, without delving too deeply into the sociological causes and consequences of individual cases.
In the European part of the globe, most societies are categorized as aging. This can be seen, among other things, in the population pyramid of Poland (Figure 3), where the largest upper part of the pyramid is expanding, which means a higher number of elderly people. This is a phenomenon characteristic of countries with low fertility rates and increasing life expectancy.
Figure 3. The population pyramid of Poland in 2023.
We deal with a balanced pyramid when there is a relative balance between successive age groups. Such an example is Turkey (Figure 4), where successive bars do not deviate significantly from each other. This shows that the fertility rate is at a relatively constant level.
Figure 4. Turkey's population pyramid in 2023.
The last basic type of population pyramids are, of course, pyramids of young societies, such as Somalia (Figure 5). The pyramid's wide base and narrow top indicate a large number of children and young people and a lower number of elderly.
Figure 5. Somalia's population pyramid in 2023.
In addition to problems with the aging or standard of living of the population, the population pyramid may also reflect situations of war or mass emigration, which will be particularly evident if we compare the pyramid to previous years (Figure 6).
Figure 6. Ukraine's population pyramid of 2018 and in 2023.
The above comparisons dealt with differences in the context of age. The population pyramid also allows for comparisons between groups, which will most often be genders. In the visualizations so far, one could see a tendency for women to live longer - the bars at the top of the pyramid were longer on the right side of the graph. In general, however, these pyramids are rather symmetrical.
However, there are societies in which this gender balance is disturbed, for example, due to state family policies. An example of such a population pyramid is the society of the United Arab Emirates (Figure 7).
Population pyramid of the United Arab Emirates in 2023.
Summary
If we add expert knowledge of sociology, demography or economics to the above analyses, the population pyramid becomes an indispensable analytical tool that visually reveals profound demographic changes in the structure of society. Its form not only captures the age and gender distribution of the population, but also reveals important trends and long-term economic and social challenges facing societies.
At the same time, it is also widely applicable to smaller samples, e.g., customers buying a particular type of product, consumers taking out loans from banks, or employees working for a particular company.
With a fixed structure, population pyramids can be easily compared with each other over time, making it easier to discover emerging trends.
[1] The charts in this chapter are based on data from the United Nations 2022 Revision of World Population Prospects report https://population.un.org/wpp/