Power and geography · 8 of 9
Demography
Read an age pyramid for what it fixes about the next thirty years.
Everybody who will be forty years old in 2065 has already been born. Nothing any government does between now and then changes that number, and it decides more about the next three decades of a country's budget than any election held during them.
The constraint
An age pyramid is a stock, in the sense the stocks and flows lesson means. Births are the flow into it, deaths are the flow out, and everybody in between moves up one row a year with no exceptions and no policy available.
The number that matters is the dependency ratio: how many people sit outside working age for every hundred inside it. It is crude, it counts a nineteen-year-old and a ninety-year-old as the same kind of dependent, and it still governs what a country can afford.
Push the years forward and watch the bulge climb. Then drag the fertility slider hard in either direction and watch the working-age population refuse to move for twenty years.
Population by five-year cohort is published for every country by the UN Population Division in the World Population Prospects, free to download. Survival rates and the shape of the presets here are stylized. The figures in the worked example come from the model on this page, which is unit tested, including the check that two very different fertility rates give identical working-age populations for twenty years.
ConventionReplacement fertility is about 2.1 children per woman rather than 2, and the extra tenth is mortality before adulthood. In countries with higher child mortality the replacement level is higher, sometimes above 3. It is also worth knowing that a population keeps growing for decades after fertility falls below replacement, because the large cohorts already born are still moving through their childbearing years. That lag is called population momentum, and it is why the turning point in a population arrives long after the turning point in its birth rate.
What the shape tells you
- Wide at the bottom. Heavy child dependency now, and a large workforce arriving over twenty years whatever anybody does. Whether that is a or a crisis depends entirely on whether jobs exist for them, and the demography does not answer that.
- A column with a bulge. The comfortable case, and temporarily. The bulge is in the workforce now and it is the same people who become dependents when it reaches the top. The good years and the bad years are the same cohort.
- Narrower at the bottom than the middle. The ratio still looks fine and the next forty years are already decided. This is the shape that produces the arguments about pensions, and the arguments arrive about twenty years after the shape does.
What to do with this
When a country's future comes up, look at the pyramid before the politics. The bulge tells you when the pension argument arrives, when the workforce peaks, and roughly how much room the government has, and none of that depends on who wins anything.
And when somebody proposes a fix, check the clock on it. Immigration works on arrival, raising participation works within a few years, and fertility works in twenty. Those are three different instruments for three different horizons, and the arguments about them are usually conducted as though they were substitutes.
Test yourself
01A country introduces generous child benefits and fertility rises immediately. When does the workforce feel it, and what happens to the budget in between?
The workforce feels it in about twenty years. The budget feels it immediately and in the wrong direction, because a baby is a dependent on the day it is born and a taxpayer two decades later. Schools, healthcare, and the benefit itself all cost money before anybody earns any.
That is not an argument against it. It is an argument that the payoff sits well outside the term of whoever passed it, which is a large part of why these policies are rare and usually underfunded.
02Immigration is often described as the fix for an aging population. What does the arithmetic actually say?
It works faster than fertility does, because an immigrant arriving at 28 is a worker on arrival rather than in twenty years. That is the whole of its advantage and it is a real one.
What it does not do is fix the ratio permanently. Immigrants age at the same rate as everybody else, so holding a dependency ratio steady through migration alone requires a rising inflow indefinitely, and the numbers get large enough to collide with politics long before they collide with arithmetic. It buys time, which is worth buying, and it is not a solution to a shape.
03Why is a country with a young population not automatically going to do well?
Because a large working-age population is a capacity rather than an outcome. It pays off if there are jobs, and it is a problem if there are not. The same demographic bulge produced the East Asian growth decades and produced unemployment and instability elsewhere, and the difference was whether the economy could absorb the people arriving. Demography sets what is possible and does not decide what happens.
A tutor that knows this lesson. It asks before it explains, and it will not tell you what to do with your own money.
Educational material, not investment or policy advice. Figures are cited where they come from a filing or a statistical series, and labelled as illustrative where they do not.