You have now met two countries in detail and four population policies. Niger, with a birth rate of 41.4 and a death rate of 8.7 per 1,000, doubling in about twenty-one years. Switzerland, with a birth rate of 8.7 and a death rate of 8.0, going almost nowhere without migration. Japan losing nearly a million people a year through natural change. Thailand, which in 1970 had a fertility rate not far below Niger's today, and now has Japan's problem.
Four countries, in four different places, apparently with nothing in common. This lesson is about the model that claims they are all on the same line, at different points along it.
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8.1.8 The demographic transition model (DTM) describes the changing levels of births and deaths in a human population through different stages of development over time.
There are five stages of the DTM, including death and then birth rates declining to produce an exponential increase, stabilization and possible decline in population.
Consider the relationship of specific age–sex pyramids to appropriate stages.
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The demographic transition model, or DTM, is a description of the order in which things happen. Its central claim is simple and slightly surprising: as a country develops, the death rate falls first, and the birth rate falls later. Everything else in the model follows from that lag.
Look at the diagram above. The top panel has the two rates you already know, and the shaded area between them is the natural increase you calculated in 1.1. The bottom panel shows what that gap does to the total population.
Stage 1: high and fluctuating. Birth rates and death rates are both high, and the death rate swings about with famine, epidemic disease and war. The two roughly cancel out, so the population stays more or less flat. No country is in stage 1 today.
Stage 2: early expanding. The death rate falls steeply while the birth rate stays high. Better food supply, clean water, sanitation and basic medicine mean far more children survive. The gap between the two lines opens wide and the population grows fast.
Stage 3: late expanding. The birth rate now falls too, and for the reasons you met in 1.2: education, later marriage, access to contraception, children costing more and surviving more reliably. The gap narrows, so the population is still growing but the growth is slowing.
Stage 4: low and fluctuating. Both rates are low and close together. Natural increase is near zero and the total population is roughly stable.
Stage 5: possible decline. The birth rate falls below the death rate. Natural change turns negative and the population falls unless something else adds people to it. An early version of the model, from 1947, already allowed for a declining stage, but most versions stopped at stage 4 until countries began to reach it. Germany's deaths have outnumbered its births every year since 1972.
The lag between the two lines is the whole model. A population does not grow in stage 2 because people suddenly start having more children. It grows because they carry on having the same number while far fewer of them die.
Task 1.1
The simulation below gives you four countries at once, drawn as anonymous birth-rate, death-rate and population curves on identical axes, using World Bank data from 1960 to 2024. Each round takes one country from each of stages 2, 3, 4 and 5. It never shows you a stage 1 country, because there are none to show. Your job is to drag each country name onto the graph you think belongs to it.
Read this before you start. The feedback tells you only how many you got right, never which. That is deliberate. It means the only way to improve is to reason from the curves, so you must write your reasoning down before you submit, not after.
https://revise.alltheway.ing/simulations/embed/crack-the-demographic-transition
Task 2.1 Choose a 6-round session. Before you submit each round, fill in one row of the table with the tell you used. Then record the score from your first lock-in, out of 4, before you try again or move on.
A reminder of what you are looking for, and how it looks in real data. Stage 2: the death rate is still falling steeply and the birth rate is still high, even if it has begun to drift down. Stage 3: the death rate has already levelled off at a low level while the birth rate keeps falling, so the gap is clearly narrower than it was. Stage 4: both rates are low and close together. Stage 5: the death-rate line sits above the birth-rate line.
| Round | The tell I used to place at least one country | Score out of 4 |
|---|---|---|
| 1 | ||
| 2 | ||
| 3 | ||
| 4 | ||
| 5 | ||
| 6 |
Task 2.2
In 1.1 you compared the age-sex pyramids of Niger and Switzerland and described their shapes. Those shapes were not a coincidence: a pyramid is a stage of the DTM seen from the side.
Think about what each stage does to the age structure.
First go to Country Profiles, click Random country, and note the country it gives you. You will classify it yourself.
Then open this comparison of Niger and Switzerland and add your random country in the Add a country box, checking the flag and name.
In the Population pyramid row, click each pyramid to open it full size and switch it to % of total before you describe its shape, so that the size difference between the countries does not distort the comparison. The birth and death rates are further down, under Changing population.
Task 3.1 Complete the empty cells of the table, then answer the questions below it. Niger's and Switzerland's rates are filled in from 1.1.
| Country | Birth rate per 1,000 | Death rate per 1,000 | Shape of the pyramid | DTM stage |
|---|---|---|---|---|
| Niger | 41.4 | 8.7 | ||
| Switzerland | 8.7 | 8.0 | ||
| Your random country |