Point the two-child limit validation page at Scorecard's rows

changelog.d/2704.changed.md

@@ -0,0 +1 @@
+Moved the two-child limit child-poverty comparison from the validation page to PolicyEngine Scorecard, which recomputes it on a certified release; the page now documents the method and links to each Scorecard row.

docs/book/validation/child-poverty-tcl.md

@@ -1,146 +1,124 @@
-# Child poverty validation: removing the two-child limit (2029-30)
+# Child poverty validation: removing the two-child limit
 
-This page compares PolicyEngine UK's estimate of the child-poverty
-impact and fiscal cost of removing the [Universal Credit two-child
-limit][gov-2cl] against the published estimates from the Department for
-Work and Pensions, the Office for Budget Responsibility and the Resolution
-Foundation. Budget 2025 announced the removal with effect from 6 April
-2026, which the
-`gov.dwp.universal_credit.elements.child.limit.child_count` parameter
-encodes (`.inf` from `2026-04-06`).
+This page sets out how PolicyEngine UK estimates the child-poverty impact
+and fiscal cost of removing the [Universal Credit two-child
+limit][gov-2cl], which Budget 2025 announced from 6 April 2026. The
+comparison with the published estimates from the Department for Work and
+Pensions, HM Treasury and the Resolution Foundation is in [PolicyEngine
+Scorecard][scorecard-lane]. Scorecard computes PolicyEngine's figures on a
+certified release, states for every row whether the two concepts match,
+and keeps the earlier runs in each row's history.
 
 Tracks [#1398](https://github.com/PolicyEngine/policyengine-uk/issues/1398).
 
-## Results
-
-| Source | Children lifted from relative low income (2029-30) | Treasury cost (2029-30) |
-|--------|----------------------------------------:|------------------------:|
-| [DWP poverty impact assessment][gov-2cl] (children); [Budget 2025, Table 1.2][budget-2025] (cost, OBR-certified) | 450,000 (AHC); 300,000 (BHC) | £3.1 bn |
-| [Resolution Foundation *No half measures*][rf-nhm] | 480,000 (AHC) | £3.5 bn |
-| **PolicyEngine UK, Microcosm UK 2024-25 (AHC)** | **~548,000** | **£3.21 bn** |
-| **PolicyEngine UK, Microcosm UK 2024-25 (BHC)** | **~460,000** | (same) |
-
-All the figures are relative low income: below 60% of the contemporary
-median. The PolicyEngine rows count HBAI dependent children
-(`is_hbai_dependent_child`), as DWP does, and were run on 23 October 2026
-on policyengine-uk 2.148.3 (main at `c65bced64`) with the certified
-Microcosm UK 2024-25 national release (`microcosm-uk-2024-25-national-20261019T083323Z-6cba5d71`, SHA-256
-`810ba980…`). On that run PolicyEngine's headcounts are above DWP's and the
-Resolution Foundation's, and its cost sits between the Budget 2025 and
-Resolution Foundation figures.
-
-On absolute low income the same run lifts ~549,000 children after housing
-costs and ~325,000 before, against DWP's 250,000 on both measures (Tables 3
-and 4). These are not like for like: PolicyEngine's absolute line is
-60% of the FYE 2025 median held constant in real terms, the reference year
-HBAI adopted in March 2026, while DWP's note predates that change and cites
-the FYE 2024 HBAI methodology, whose line is 60% of the FYE 2011 median.
-
-Earlier versions of this page reported ~463,000 (AHC) and ~336,000 (BHC)
-children and £3.26 bn on an earlier Microcosm UK release (SHA-256
-`aa31bdf6…`, policyengine-uk 2.123.7), and ~501,000, ~415,000 and £3.40 bn
-on the Enhanced FRS 2022-23 in May 2026. The snippet those versions showed
-computed only the after-housing-costs figure, using `in_poverty_ahc`
-(absolute low income) and counting children with `is_child` (everyone under
-18), so at least those figures are not comparable with the relative
-benchmarks above; the code for the before-housing-costs figures was not
-shown.
-
-## How the estimate was produced
+## The comparison in Scorecard
+
+| Benchmark | Scorecard row |
+|---|---|
+| DWP: children in relative low income, after housing costs, FYE 2030 (Table 1) | [row][dwp-rel-ahc] |
+| DWP: children in relative low income, before housing costs, FYE 2030 (Table 2) | [row][dwp-rel-bhc] |
+| DWP: children in absolute low income, after housing costs, FYE 2030 (Table 3) | [row][dwp-abs-ahc] |
+| DWP: children in absolute low income, before housing costs, FYE 2030 (Table 4) | [row][dwp-abs-bhc] |
+| DWP: children in gaining households, FYE 2030 | [row][dwp-gainers] |
+| HM Treasury: static Exchequer cost, 2029-30 | [row][hmt-static] |
+| HM Treasury: post-behavioural cost, 2029-30 (the £3.1 billion in Budget 2025 Table 1.2) | [row][hmt-post] |
+| Resolution Foundation, *No half measures*: children, 2029-30 | [row][rf-children] |
+| Resolution Foundation, *No half measures*: cost, 2029-30 | [row][rf-cost] |
+
+Each row shows the published figure, PolicyEngine's value, the comparison
+status and the notes that explain it. Two notes matter most:
+
+- **The absolute line.** DWP's note uses the FYE 2011 reference year (60%
+  of the FYE 2011 median, held constant in real terms). PolicyEngine UK's
+  `in_poverty_*` use the FYE 2025 reference. The FYE 2011 line is
+  `in_absolute_poverty_fye2011_*` from policyengine-uk 2.155.0. The
+  certified release Scorecard runs on predates that, so Scorecard
+  constructs the FYE 2011 line for the comparison.
+- **Static and post-behavioural costs.** PolicyEngine's cost is static, so
+  it compares with HM Treasury's static leg. The £3.1 billion includes a
+  behavioural adjustment.
+
+Scorecard also records a [decomposition][decomposition] of how the
+estimate moved between PolicyEngine's September and October 2026 figures:
+how much came from the data, the model version, the child count and the
+relative-line convention, and which policyengine-uk releases moved it.
+
+## The reform
+
+The `gov.dwp.universal_credit.elements.child.limit.child_count` parameter
+is 2 from 6 April 2017 and infinite from 6 April 2026. Current law already
+removes the limit, so the estimate compares two worlds: current law, and
+current law with the parameter set back to 2. The effect of removing the
+limit is current law minus that with-limit world. A year `Y` in
+PolicyEngine UK is the financial year that starts in April `Y`, so FYE
+2030 is `2029`.
+
+## The measures
+
+- **Relative low income**: `in_relative_poverty_ahc` and
+  `in_relative_poverty_bhc`. These flag equivalised HBAI household income
+  below 60% of the median of the world being calculated, with the median
+  taken over people.
+- **Absolute low income**: `in_poverty_ahc` and `in_poverty_bhc`. From FYE
+  2022 these use 60% of the FYE 2025 median, held constant in real terms.
+  `in_absolute_poverty_fye2011_ahc` and `in_absolute_poverty_fye2011_bhc`
+  use the FYE 2011 median in every year, the line in DWP's note.
+- **Children**: `is_hbai_dependent_child`, HBAI's dependent children, as
+  DWP counts them.
+- **Cost**: the change in `gov_balance` (tax less spending). The estimate
+  is static: the labour-supply elasticities are zero, and `would_claim_uc`
+  is a data input, so neither work nor take-up responds to the reform.
 
 ```python
-from policyengine_uk import Microsimulation
-
-# Local path to the Microcosm UK 2024-25 national release file.
-DATASET = "microcosm_uk_2024_25.h5"
-YEAR = 2029  # fiscal year 2029-30
-
-# Current law baseline (TCL removed from 2026-04-06 per Budget 2025)
-sim_baseline = Microsimulation(dataset=DATASET)
-
-# Counterfactual where the TCL is held in place at 2 children
-sim_counter = Microsimulation(
-    dataset=DATASET,
-    reform={
-        "gov.dwp.universal_credit.elements.child.limit.child_count": {
-            f"{YEAR}-01-01": 2,
-        },
-    },
-)
+import policyengine as pe
+
+YEAR = 2029  # FY 2029-30 (FYE 2030)
+LIMIT = "gov.dwp.universal_credit.elements.child.limit.child_count"
 
-# HBAI dependent children, as in DWP's statistics.
-is_child = sim_baseline.calculate("is_hbai_dependent_child", YEAR)
+current_law = pe.uk.managed_microsimulation()
+with_limit = pe.uk.managed_microsimulation(reform={LIMIT: {"2025-01-01.2035-12-31": 2}})
 
-for measure in ["in_relative_poverty_ahc", "in_relative_poverty_bhc"]:
-    baseline = sim_baseline.calculate(measure, YEAR, map_to="person")
-    counter = sim_counter.calculate(measure, YEAR, map_to="person")
-    lifted = ((counter.astype(float) - baseline.astype(float)) * is_child).sum()
-    print(f"{measure} children lifted: {lifted / 1e3:.0f}k")
+children = current_law.calculate("is_hbai_dependent_child", YEAR)
+for measure in ("in_relative_poverty_ahc", "in_relative_poverty_bhc"):
+    lifted = (
+        with_limit.calculate(measure, YEAR, map_to="person").astype(float)
+        - current_law.calculate(measure, YEAR, map_to="person").astype(float)
+    ) * children
+    print(measure, lifted.sum())
 
-fiscal_cost = (
-    sim_counter.calculate("gov_balance", YEAR).sum()
-    - sim_baseline.calculate("gov_balance", YEAR).sum()
+cost = (
+    with_limit.calculate("gov_balance", YEAR).sum()
+    - current_law.calculate("gov_balance", YEAR).sum()
 )
-print(f"Treasury cost: £{fiscal_cost / 1e9:.2f}bn")
+print("cost", cost)
 ```
 
-This is a *reverse* comparison: PolicyEngine's baseline already includes
-the TCL removal (the parameter flips to infinity from 2026-04-06), so the
-counterfactual *re-imposes* the limit at 2 children to compute the
-2029-30 effect. The signs cancel out: the children-lifted figure is
-positive (baseline has fewer in poverty than counterfactual) and the
-Treasury cost is positive (the baseline pays more Universal Credit, so its
-`gov_balance`, tax less spending, is lower than the counterfactual's).
-
-## Why the estimates differ
-
-Three plausible drivers of the remaining differences:
-
-1. **Nowcasting methodology**. RF projects incomes with its own nowcast,
-   with private rents rising in line with average earnings after a
-   12-month lag and its own after-housing-costs deflator; DWP uses its
-   static Policy Simulation Model on the FRS for FYE 2022 to 2024 with its
-   caseload forecasts. See the
-   [PolicyEngine vs RF comparison](../assumptions/nowcasting-comparison.md)
-   and the [RF methodology detail](../assumptions/rf-nowcasting-methodology.md)
-   for where PolicyEngine's nowcasting differs from RF's.
-2. **Take-up assumptions**. PolicyEngine decides Universal Credit claims
-   with flags set in the data, which do not respond to the reform: a family
-   claims if `would_claim_uc` is true, or if DWP has moved it off a closed
-   legacy benefit it reports (tax credits, Income Support or income-based
-   Jobseeker's Allowance; `legacy_benefits_closed`, which leaves out
-   families sent to Pension Credit instead) and
-   `would_claim_uc_at_legacy_closure` is true.
-   The data set `would_claim_uc` for every family that reports Universal
-   Credit and draw it at a residual rate for the rest, so newly entitled
-   families claim at that residual rate unless they reported a closed
-   legacy benefit. A
-   source that assumes lower take-up among newly entitled families would
-   show a smaller headcount and cost.
-3. **Data and calibration vintage**. The DWP and OBR estimates were
-   finalised against the OBR's November 2025 forecast, and RF's
-   (30 October 2025) against the OBR's March 2025 earnings forecast and the
-   Bank of England's August 2025 inflation forecast; PolicyEngine's
-   parameters tick over with each EFO release. The Microcosm release is
-   built from FRS 2024-25, with take-up anchored on reported receipt.
-
-## How to keep this validation alive
-
-- Re-run the snippet on each new Microcosm UK release, and when the
-  remaining `would_claim_*` conversions (#1621) land. Both could move the
-  AHC poverty rate by a non-trivial amount.
-- After each new EFO release, update the per-year poverty headcounts and
-  the fiscal cost table.
+`pe.uk.managed_microsimulation()` loads the dataset pinned by the
+installed policyengine.py release. Each release certifies that dataset
+with one policyengine-uk version, which `policyengine[uk]` installs:
+6.11.0, the release Scorecard uses, pins policyengine-uk 2.132.6. Scorecard's
+[`compute_uk_two_child_limit_poverty.py`][compute] runs the same
+comparison for every year, measure and group the benchmarks use.
 
 ## References
 
-- HM Treasury, [Budget 2025][budget-2025], Table 1.2: the OBR-certified cost of removing the two-child limit (£3.1 billion in 2029-30).
-- OBR, [Economic and Fiscal Outlook November 2025][obr-efo].
+- DWP, [Removing the two-child limit on Universal Credit: impact on low income poverty levels in the United Kingdom][gov-2cl] (26 November 2025), Tables 1 to 4.
+- HM Treasury, [Budget 2025][budget-2025], Table 1.2.
 - Resolution Foundation, [No half measures: setting child poverty on a downward course at the Autumn Budget][rf-nhm] (30 October 2025).
-- DWP, [Removing the two-child limit on Universal Credit: impact on low income poverty levels in the United Kingdom][gov-2cl], Tables 1 and 2 (relative low income) and 3 and 4 (absolute low income), financial year ending 2030.
 - Issue: [#1398](https://github.com/PolicyEngine/policyengine-uk/issues/1398). Related: [#1171](https://github.com/PolicyEngine/policyengine-uk/issues/1171), [#1388](https://github.com/PolicyEngine/policyengine-uk/issues/1388).
 
-[obr-efo]: https://obr.uk/efo/economic-and-fiscal-outlook-november-2025/
+[gov-2cl]: https://www.gov.uk/government/publications/poverty-impacts-of-social-security-changes-at-budget-2025/removing-the-two-child-limit-on-universal-credit-impact-on-low-income-poverty-levels-in-the-united-kingdom
 [budget-2025]: https://www.gov.uk/government/publications/budget-2025-document/budget-2025-html
 [rf-nhm]: https://www.resolutionfoundation.org/publications/no-half-measures/
-[gov-2cl]: https://www.gov.uk/government/publications/poverty-impacts-of-social-security-changes-at-budget-2025/removing-the-two-child-limit-on-universal-credit-impact-on-low-income-poverty-levels-in-the-united-kingdom
+[scorecard-lane]: https://www.policyengine.org/scorecard/?country=uk&view=validation
+[dwp-rel-ahc]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=2f90d6562b5cf8008c94
+[dwp-rel-bhc]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=d840d48b5aa86092e053
+[dwp-abs-ahc]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=0953bfed29bf91c21076
+[dwp-abs-bhc]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=f0db70b0fc559137b2b8
+[dwp-gainers]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=c95c29a868535490a0e4
+[hmt-static]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=67f3e4d6a1070d902798
+[hmt-post]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=97d6c677b464338f8233
+[rf-children]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=5cd40f11fde6cd6df668
+[rf-cost]: https://www.policyengine.org/scorecard/?country=uk&view=validation&claim=a05d61066f4bc096db86
+[decomposition]: https://github.com/PolicyEngine/policyengine-scorecard/blob/main/results/uk/two_child_limit_poverty/DECOMPOSITION.md
+[compute]: https://github.com/PolicyEngine/policyengine-scorecard/blob/main/pipeline/compute_uk_two_child_limit_poverty.py

docs/book/validation/reform-impacts-dashboard-plan.md

@@ -167,8 +167,9 @@ Add to v2 over time as published OBR / RF reforms become available
 benchmarks:
 
 - Reinstate the two-child limit. The baseline removes it from 6 April
-  2026, and [child-poverty-tcl.md](child-poverty-tcl.md) compares its
-  removal with the DWP, Budget 2025 and Resolution Foundation estimates.
+  2026, and [child-poverty-tcl.md](child-poverty-tcl.md) links to
+  Scorecard's comparison of its removal with the DWP, HM Treasury and
+  Resolution Foundation estimates.
 - Freeze the Personal Allowance for an additional year (to 2031-32, so
   it needs a later reference year than 2029).
 - 1pp employer NI change.
@@ -197,7 +198,7 @@ relevant pages are:
 
 - [nowcasting-comparison.md](../assumptions/nowcasting-comparison.md) (PolicyEngine vs RF).
 - [rf-nowcasting-methodology.md](../assumptions/rf-nowcasting-methodology.md) (RF methodology detail).
-- [child-poverty-tcl.md](child-poverty-tcl.md) (the child-poverty impact and cost of removing the two-child limit, against DWP, Budget 2025 and Resolution Foundation estimates).
+- [child-poverty-tcl.md](child-poverty-tcl.md) (how PolicyEngine UK estimates the child-poverty impact and cost of removing the two-child limit, with links to Scorecard's comparison against DWP, HM Treasury and Resolution Foundation estimates).
 
 ## Open questions
 

docs/book/validation/two-child-limit-full-rollout.md

@@ -4,7 +4,9 @@ This page shows how to reproduce published estimates of reforming the
 Universal Credit two-child limit that assume the limit is **fully rolled
 out**, such as the IFS Green Budget 2025 comment [Options for reforming the
 two-child limit][ifs-2025], and how PolicyEngine UK's results compare. For
-the 2029-30 comparison with DWP, OBR and Resolution Foundation estimates, see
+how PolicyEngine UK estimates removing the limit in 2029-30, with links to
+Scorecard's comparison against DWP, HM Treasury and Resolution Foundation
+estimates, see
 [Child poverty validation: removing the two-child limit](child-poverty-tcl.md).
 
 ## Settings that matter