The Ledger · Far — twenty to thirty-five years

From The Rational Prophet (Book Four of The Laws of Game Theory)

The bet

The bet

In states spending more than three per cent of GDP on family benefits for a decade, the women born in 2007 to 2009 — the first generation still under twenty when this book went to press — end their fertile years no more than 0.2 children above the level before the policy began. The money moves when children are born, not how many.

Win

No qualifying state exceeds its pre-policy level by more than 0.2.

Lose

One does.

Expiry

2054, when the youngest of the three cohorts reaches forty-five — twenty-eight years — read from the first release that publishes that year's rates.

Check it

Eurostat's fertility rates by age, free, for completed cohort fertility, with the French statistics office, INSEE, for France; the OECD family database for spending.

In protocol form

Word for word from Appendix D of the book, the Prediction Protocol, where this bet is entered as Cohort fertility. References to sections (§) are to that appendix.

Universe

states whose family benefit spending exceeded three per cent of GDP in each of the ten most recent years published at the time this book went to press, in the series that combines cash, services and tax measures. A year with no published value is passed over: it neither qualifies nor disqualifies a state. The window looks backwards, and it has to: a universe defined by a future condition cannot be listed on the day the bet is made, and a list assembled later is a list assembled knowing something. The qualifying states are printed with the baseline and do not change afterwards, whatever happens to their spending during the window.

Source

Eurostat's fertility rates by single year of age, free and without registration, for completed cohort fertility; for France, whose series there begins too late for its pre-policy cohorts, the French statistics office's (INSEE's) table of cumulative fertility by age and year of birth for metropolitan France; the OECD Family Database, family benefits public spending as a share of GDP, for the universe test.

Definitions

completed cohort fertility is the sum of a birth cohort's age-specific rates from the youngest published age up to and including forty-five, each read in the year the cohort reaches that age. For the pre-policy cohorts, an age with no published rate counts as zero. For a scored cohort, any age without a published rate means the cohort has no published figure. The policy start for a state is the first published year of the unbroken run of published years above three per cent of GDP that qualified it, passing over unpublished years — not the year a programme was announced, and not the year a minister first used the word, because both are arguable and the spending series is not. Where the run begins with the first year the series publishes, that year is the policy start. The pre-policy level is the average completed fertility of the three cohorts that reached forty-five before the policy start. A level is used rather than a trend, because the cohorts scored are some fifty years younger, and a straight line carried that far says nothing. The scored cohorts are the women born in 2007, 2008 and 2009. They were under twenty when this book went to press, so nothing of their fertility after twenty was known to the author, and all their fertile years from twenty fall after the policy start in every qualifying state. Older cohorts are not scored, because part of their answer was already visible. Each qualifying state's policy start, pre-policy cohorts and pre-policy level are printed with the baseline, and none of them moves afterwards.

Calculation

the average completed fertility of the three scored cohorts minus the pre-policy level; threshold 0.2. The reading is made from the first release of the source that publishes the rates for 2054, the year the youngest scored cohort reaches forty-five. A qualifying state with no published figure for a scored cohort at the reading counts as exceeding the threshold: missing evidence counts against the prediction.

Baseline

policy start, pre-policy cohorts and pre-policy level per qualifying state, calculated and printed.

Known weakness

a level does not follow a falling trend. If fertility keeps falling everywhere, for reasons that have nothing to do with the money, the bet becomes easier to win, and a hit proves less. A comparison with states that never qualified would answer that objection. It is not attempted here.

Scope

this is a claim about transfers. The universe is set by the spending rule alone, and a state whose fertility runs through an identity channel does not refute it.

Baseline at publication

Reading date of record: 10 October 2026

What is recorded

The list of qualifying states · policy start, pre-policy cohorts and pre-policy level, each state

Value at publication

Qualifying states (OECD Family Database, public spending on family benefits, edition updated February 2025; total of cash, services and tax measures above 3% of GDP in every published year 2012–2021, France's unpublished 2012 passed over): Belgium, Denmark, France, Iceland, Luxembourg, Sweden. Policy start · pre-policy cohorts · pre-policy level, completed fertility to age 45 from Eurostat (France: INSEE, metropolitan France): Belgium 2007 · 1959–1961 · 1.86; Denmark 2001 · 1953–1955 · 1.85; France 2001 · 1953–1955 · 2.12; Iceland 2007 · 1959–1961 · 2.47; Luxembourg 2008 · 1960–1962 · 1.76; Sweden 2002 · 1954–1956 · 2.03. For Denmark and France the policy start is the first year the spending series publishes (read 10 October 2026)

Author’s probability 85% that this bet scores HIT. Registered on 10 October 2026.

Sources

• OECD Family Database, public spending on family benefits
• INSEE, cumulative fertility by age and year of birth

Not investment advice. The bet describes what the book expects to happen; nothing here is a recommendation to buy, sell or hold anything.

Last reviewed 10 October 2026