The DTM Explorer

Two lines and one gap

You met the development indicators in the measuring module. This one is about the Demographic Transition Model, and it is easier than it looks once you see what it actually is. It is two lines on the same diagram. One is the birth rate, one is the death rate, and the population total depends on neither of them on its own. It depends on the GAP between them. Almost every mark lost on this model is lost by reading one line when the question is about the gap, and the place it happens is stage three.

Rates and what they mean

Six terms. The third is the one that makes sense of everything else.

The five stages in order

Put the five stages of the model into the order the model sets out.

• Both rates are high, so the total stays low and unsteady
• The death rate falls while births stay high, so the total climbs steeply
• The birth rate now falls too, so the total still climbs but more slowly
• Both rates are low, so the total is high and roughly steady
• The birth rate drops below the death rate, so the total may start to fall

Stage to what the rates do

Why the total keeps rising

In stage three the birth rate is falling. Why does the population total still go up?

• Because the birth rate is still above the death rate, so there is still a gap
• Because the death rate is rising at the same time as the birth rate falls
• Because people are moving into the country and adding to the total
• It does not; the population falls as soon as the birth rate starts to drop

Read the gap, not the line

Here is the sentence to keep. The population grows whenever the birth rate is ABOVE the death rate, however fast the birth rate happens to be falling. Falling is about direction; growing is about position. So when a question gives you a stage and asks what happens to the population, do not look at whether a line is going down. Look at which line is on top and how far apart they are. That one habit answers stage two, stage three and stage five without any further thinking.

Plot the falling death rate

This is a SCHEMATIC diagram of the model, not data about any real country: the vertical scale is simply higher for a higher rate. The birth rate is already plotted across stages 1 to 4, staying high and then falling. The death rate is plotted at stage 1 and stage 3. **Plot the death rate at stage 2**, remembering that in stage 2 the death rate is falling steeply while births stay high.

Why deaths fall first

In stage two the death rate falls before the birth rate does. Select the TWO reasons that explain the fall in DEATHS.

• Cleaner water supplies and better sanitation
• A more reliable food supply and better nutrition
• Wider availability of contraception
• More women staying in education and paid work

The model in a paragraph

The model plots two lines. Where the birth rate sits above the death rate, the gap between them is the natural _____, and the total population _____. In stage two the death rate falls while births stay high, so the gap is at its _____. In stage three the birth rate falls as well, so the gap _____ and growth slows without stopping. Only when the birth rate drops below the death rate does the total begin to _____.

What the model leaves out

A model is a simplification, and saying what it simplifies away is not criticism of it. It is the second half of knowing what it is.

The people it cannot see

A country in stage four has a birth rate and a death rate that are almost equal, yet its population is growing noticeably. What is the most likely explanation, and what does it show about the model?

• More people are moving in than leaving, which the model does not account for
• The country must actually be in stage two rather than stage four
• The model is wrong, since a stage four population cannot grow at all
• The rates must have been measured incorrectly for that country

Explaining stage three

Question: explain what happens to the population of a country in stage three of the Demographic Transition Model. Model answer: in stage three the birth rate falls, for reasons such as wider access to contraception and more women staying in education and paid work, while the death rate stays low. Because the birth rate is falling towards the death rate rather than below it, the two lines move closer together but the birth rate is still the higher of the two. That gap is the natural increase, so the population continues to grow, but more slowly than in stage two when the gap was at its widest. It is worth adding that the model describes natural change only, so a country in stage three whose population is growing faster or slower than the model suggests may be gaining or losing people through migration. Notice that the answer explains the gap before saying what the total does, and then reaches for one limit of the model rather than describing all five stages.

Which reading is wrong

Three of these statements read the model correctly. Select the ONE that does not.

• In stage two the gap between the lines is at its widest, so growth is fastest.
• In stage three the birth rate is falling, so the population is falling as well.
• In stage four both rates are low, so the total is high and roughly steady.
• The model shows natural change only, so migration can move a real total away from it.

Placing a country

You are given rate information about four situations and asked to use the model. Work through them.

• Deaths have fallen sharply over recent decades while births have stayed high. Which stage does the model suggest?
• What does the model predict about that population total?
• A second place has a birth rate slightly below its death rate. What does the model say?
• That second place is in fact growing. What should your answer say?

Explain the model

Explain how the Demographic Transition Model accounts for changes in population, and assess how useful it is.

• Explain what the two lines on the model are, and what the gap between them represents
• Explain what happens to the population in stage two, and why growth is fastest there
• Explain why the population continues to grow in stage three even though births are falling
• Give one reason the death rate falls in stage two and one reason the birth rate falls in stage three
• Give one limit of the model, and explain what it means for using the model on a real country
• Reach a judgement on how useful the model is, with a reason