Population Decline’s Positive-Case Search: A Pre-Registered Falsification Test

Verbatim from the registry.

Pre-registered 2026-05-07:

No OECD country currently in sub-replacement fertility (period TFR < 1.7 in 2024) will produce sustained cohort fertility recovery to ≥ 1.70 for women born 1990-1995 via primarily-policy means — defined as pronatalist spending and family-policy expansion absent structural-cultural shift in the housing/working-hours/gender-norms/neighborhood-child-density/intergenerational-caregiving substrate — over the 2025-2035 observation window.

Falsifier (any one of):

1. Cohort fertility ≥ 1.70 for women born 1990-1995 (cohort completion data ~2030-2035, varying by country) in any country that was sub-replacement at start of window AND where the dominant wedge variable is identifiable as policy spend rather than structural-cultural shift.
2. Tempo-adjusted period TFR (Bongaarts-Feeney) sustained ≥ 1.70 for 5 consecutive years across 2025-2035 in any sub-replacement country with the same wedge profile.
3. A pronatalist policy package implemented within the window that produces, by 2035, > 0.40 sustained cohort fertility lift in any single country, attributable post-hoc to policy rather than structural co-shift, by independent demographic analysis (e.g., N-IUSSP, AEI Demographics, Wittgenstein Centre).

Resolution: 2035 OECD Family Database / Human Fertility Database cohort completion releases, supplemented by country-level statistics agencies and independent demographic-research bodies. The verdict will be issued in v2 of this finding with a what-changed banner pointing to v1.

Eight candidates, eight bands, one meta.

The eight watch-list countries cluster sub-replacement (Israel excepted). Their period TFR trajectories 2010-2024 are below. The falsification test asks whether any of them produces a cohort lift the period series would not predict.

The scatter below sets pronatalist spending intensity (% GDP, current period) against TFR change 2010-2024. If spending were the lever, the cluster would trend up-and-to-the-right. It does not. Hungary’s small positive ticks the highest spending bracket but is interpretable as tempo (the Korea-Hungary finding documents this). Israel’s high TFR sits far left — low spending — because the wedge is religious-community structure.

Per-country predictions

The cohort projections below are conservative central estimates derived from the 2024 period TFR trajectory minus tempo-share, plus modest cohort drift assumptions consistent with the literature. The falsifier bands are intentionally wide — wide enough that we cannot dismiss a real cohort lift as noise.

The Israel prediction is the load-bearing contrast: predicted above 1.70 but not a falsification, because the wedge is structural-cultural (religious-community substrate), not policy spend. The prediction architecture forces this distinction explicit. If a reader wants to argue Israel falsifies the finding, they have to argue Israeli pronatalist policy is doing the heavy lifting — a position no demographer of Israel actually holds.

Pending resolution.

Pending resolution.

The contingent research path.

If held

The thesis hardens from claim to structural feature of the policy space. The next finding becomes a constructive program: the 1990-1995 cohort having completed sub-replacement, what does the demographic adaptation playbook look like? That research direction reframes the field from “how do we restore replacement?” to “how do we structure institutions for permanent population contraction without mass welfare collapse?” — the question Korea, Italy, and Japan are already running natural experiments on. A held verdict is not a counsel of despair; it is a redirection of research dollars from policy-spend optimization to structural-condition rebuilding (housing supply, working-time policy, gender-equity hours-gap reduction, neighborhood child-density restoration) on multi-generational time horizons.

If overturned

The overturning case becomes the new study target. Form 1 (Detective story) is the right form for the follow-up: which suspect mechanism explains the disconfirming case? Pronatalist spending is unlikely to be the only operative variable even if the policy attribution is clean — something else co-shifted that we did not name in the wedge taxonomy. The retraction note for v2 names that something. The Korea-Hungary v1 finding is jointly re-examined; if its tempo-without-cohort interpretation also fails for the new positive case, the static-version finding moves to revised lifecycle and a v2 incorporates the new mechanism.

If partial

The most likely actual path: a country crosses the threshold but demographers split on whether the wedge is policy or co-shifted. v2 narrows to the cleanly-held subset; v3 pre-registers tighter conditions on the contested case (e.g., “by 2040 the lift sustains under continued policy AND no further structural shift,” which adds another decade of resolution time but extracts the policy-isolation question).

Anti-goalpost-moving commitments, pre-registered.

The most common failure mode of falsification claims in social science is moving the goalposts at resolution. The following commitments are made now, while we still don’t know the answer, so that future-us cannot save the finding by quietly redefining the test.

What we are explicitly NOT going to count as a save

• Tempo-adjusted period TFR rising temporarily. The Korea-Hungary finding documented the tempo-without-cohort failure mode. We commit: tempo-adjusted period TFR ≥ 1.70 for fewer than 5 consecutive years does not save the finding. Cohort completion data is the gold standard.
• Cohort projections that are not yet complete. The 1990-1995 cohort begins reaching age 45 around 2035. Until at least 90% of the cohort has reached age 45, projections are interim. We commit: only completed cohort fertility (or cohort fertility for women aged ≥ 42 with ≤ 5% upward revision plausible) counts as resolution data.
• Country-specific exemptions for measurement difficulty. Migration creates noise in cohort fertility for Germany, Sweden, and France. We commit: the published cohort fertility from the Human Fertility Database / national statistics agency at the resolution date counts as the official value, regardless of post-hoc adjustment proposals.
• Wedge re-attribution after resolution. If a country crosses 1.70 and the wedge looks structural-cultural rather than policy, that is a finding-saving condition; we accept that. But: the structural-cultural attribution must be issued by an independent demographic body within 24 months of resolution, not by the Lab itself, and not retroactively expanded to capture borderline cases.
• Outcome-favorable reframing of the candidate set. The watch list is fixed at 8 countries at v1. If a country we did not include (say, Iran or Tunisia, both in fertility transition) crosses 1.70 in cohort terms, that is interesting but it is not a falsifier of this particular finding (which named OECD sub-replacement countries). v2 will pre-register a separate finding for non-OECD candidates if the question warrants.

Falsifier sensitivity

The TornadoPlot below visualizes how the verdict shifts under different (non-pre-registered) bar choices. Reading: lower-bar choices (loose) make the finding easier to overturn; upper-bar choices (strict) make it easier to defend. The committed bar sits at the calibration the original Korea-Hungary thesis named. We bind ourselves to that bar.

Cohort distance from the bar

Open questions adjacent to this test.

• The structural-cultural substrate question. If policy is not the lever and structural-cultural conditions are, what specifically about the substrate matters most? Working-hours policy? Housing affordability? Gender hours-gap inside marriages? Neighborhood child-density? Each is independently testable against cross-country variance. The next finding in this domain operationalizes one of them.
• The asymmetry mechanism. Cultural-structural conditions take generations to build, can be lost in a generation. What specifically produces this asymmetry? Coordination-equilibrium dynamics (everyone has to expect everyone else)? Infrastructure decay outpacing infrastructure construction? Cohort-cohort transmission of expectations? This is the build/destroy asymmetry mentioned in the load-bearing thesis; it deserves its own Form 4 (Pattern across cases) finding.
• Israel as the constructive positive case. If religious-community structure is the operative wedge, what specifically about that structure is the lever? Marriage timing? Community child-care infrastructure? Status reward for parenthood? Fertility transmission within sub-communities? Pre-registering a constructive (non-falsification) finding on Israel’s fertility mechanism would test whether the structural-cultural lens has positive predictive content, not just negative.
• The 2040+ horizon. If the 2030-2035 verdict holds, the next pre-registration extends to the 1995-2000 cohort (completing ~2040), which will have lived through a different policy environment (post-Korean lowest-low, post-Hungarian retreat, post-Japan policy expansion). The question for v3 of this finding: does the policy-versus-structural conclusion hold across cohorts that grew up under explicitly more pronatalist regimes?
• Cross-domain replication. The necessary-but-insufficient framing should generalize beyond fertility. Trust networks, religious participation, civic engagement — all are coordination-equilibrium phenomena where policy can compensate at margins but not create the substrate. A Form 4 finding that documents the asymmetry across multiple substrate phenomena would strengthen the population-decline finding by establishing the mechanism’s broader scope.

Cross-references

This finding is the operationalized falsification test of lab:finding/popdec/2026/korea-hungary-divergence/v1 (the static thesis) and lab:finding/popdec/2026/korea-lockin/v1 (the dynamic thesis). All three should be read together. Reading any one without the others weakens the structural argument; reading them together makes it bulletproof.