1.3 Population pyramids

One commonly used type of back-to-back chart is the population pyramid. A population pyramid is made up of two vertical, back-to-back histograms which show how the population of an area falls into different age categories. The bars of the histogram can be drawn to show either the size of the population, or the percentage of the total population. Note the change to the word ‘histogram’ here because we are now talking about grouped numerical data.

Here is the population pyramid for the United Kingdom (UK) in 1960:

One comparison you can make is between the male population (orange bars) and female population (green bars). The pyramid is almost symmetrical, but you might have noticed that the orange bars are a little larger than the green bars at the base of the pyramid, and shorter at the top. This matches with some interesting facts about the UK population: slightly more boys than girls are born each year, and the life expectancy of a typical female is longer than that of a male.

You may also notice dips in the population, around age groups 20 – 29 and 40 – 44. I wonder if you can think of any possible reasons for dips in the UK population in these age ranges in 1960.

Asking learners to make conjectures about data in this way helps give the data meaning through context. In UK history lessons learners study World Wars I and II and, possibly, the subsequent ‘baby booms’ that followed these events.

Records of historical data can be found online but there is increasing availability of animated visual representations, and these can be a useful learning tool for exploring graphical representations and identifying trends in data. For instance, this UK population pyramid interactive created using UK Census data: UK population pyramid interactive - Office for National Statistics (ons.gov.uk, 2020). It is worth taking time to explore and consider the additional comparisons and analysis made possible by these.

When working with statistics, you may see datasets which implicitly present sex/gender as a binary option between ‘male/man’ and ‘female/woman’ and makes no distinction with assigned sex at birth in this classification.

In the teaching of statistics specifically, framing sex/gender as a binary has, for many years, been seen uncontroversially as a useful teaching tool for helping learners get to grips with the concept of binary variables, and datasets using them.

Consequently, you will come across lots of examples using real data, where only binary sex/gender data was collected, reflecting the thinking of the time.

However, at the Open University we now recognise a much broader diversity of belief around sex and gender beyond the male/female binary.

The Office for National Statistics (ONS) census data included a non-binary question on gender for the first time in 2023 and found that 0.05% of the UK population described themselves as non-binary.

Although ‘population pyramids’ do not always turn up in the mathematics syllabus, back-to-back bar charts do and clearly, they are a form of these. Population pyramids do occur in other subjects, such as statistics and geography, and they offer a good opportunity to strengthen interpretation of graphical representations and to connect learning with actual data and using large datasets.

Population pyramids can give rise to rich statistical questions and learning opportunities, but their shapes can also reflect serious issues including gender bias, reproductive rights, and the consequences of armed conflict. It is important not to shy away from difficult topics, but topical issues should be handled with care with learners of all ages. Learners are naturally inquisitive and want to know more about the world around them, especially potentially controversial topics!

Just as literature tells a story, so does data, and it is important that learners are taught to critically reflect and analyse that data. Take it as an opportunity to work collaboratively with other teachers, identifying potential complexities and working through strategies for managing sensitive conversations in the classroom. Colleagues in history, geography and the social sciences will all deal with tough topics in their classrooms on a regular basis.