Demographics

Most economic variables are hard to forecast a year out. The age structure of a population in 2050 is largely known now, because almost everyone who will be over twenty-five then is already alive. It is the one long-range forecast that is reliable, and it is almost entirely absent from market commentary.

The arithmetic of growth

Wealth Signal calculation

Two components, and one of them is fixed
GDP growth ≈ growth in the number of workers + growth in output per worker. An economy whose working-age population shrinks 0.5% a year needs productivity growth above 0.5% simply to avoid contracting. That is not a policy failure when it happens; it is subtraction.

The dependency ratio

The ratio of people outside working age — young and old — to those within it. A high young-dependency ratio is a future investment: those children become workers. A high old-dependency ratio is a present cost, met through pensions, healthcare and care services.

The transition between the two produces a demographic dividend: a period when the birth rate has fallen but the large cohort born earlier is still working, so the dependency ratio is unusually low. Several of the fastest sustained growth episodes in modern history coincided with that window, which closes on schedule.

The contested effects

On interest rates. One argument: a large cohort saving for retirement increases the supply of savings, pushing rates down; when that cohort retires and spends, the flow reverses. Both halves are plausible; the empirical work disagrees about magnitude.
On inflation. One view holds that a shrinking workforce is inflationary, since scarce labour bids up wages. Another holds that ageing populations spend less, which is disinflationary. Different countries have provided evidence for both.
On asset prices. The suggestion that a retiring cohort selling assets depresses prices has been made for decades. Retirees draw down slowly, bequests transfer assets rather than liquidating them, and global capital markets mean domestic demographics need not set domestic asset prices.

Interpretation

The direction is clearer than the magnitude, and the timing is clearer than either
Demographic effects are slow, cumulative and swamped in any given year by the business cycle. This makes them nearly useless for investment timing and genuinely important for thirty-year questions: pension adequacy, government debt trajectories, healthcare demand, and which countries face contraction without immigration.

The pension mathematics

Pay-as-you-go systems fund current pensions from current workers' contributions. That requires a stable ratio between the two groups. When the ratio deteriorates, exactly four adjustments are available: higher contributions, lower benefits, later retirement, or more workers through immigration or participation. Every national pension debate is a rearrangement of those four, and there is no fifth.

Migration

Migration is the fastest available adjustment to a demographic shortfall and the most politically contested. Economically, migrants of working age improve the dependency ratio immediately and age into it themselves later, so it is a deferral as well as a fix. The politics are outside the scope of this lesson; the arithmetic is not complicated.

Demographics explain a lot about differences between countries over decades and almost nothing about differences between quarters. Use accordingly.

Education, not advice. These lessons explain how things work. They do not tell you what to buy, and Wealth Signal does not publish recommendations. Full disclaimer.