Refresh social rent target to EHS 2024-25 vintage

changelog.d/social-rent-target-vintage.fixed.md

@@ -0,0 +1 @@
+Refresh the social rent calibration target to the English Housing Survey 2024-25 mean (GBP 129/week, from GBP 118/week in EHS 2023-24). The target is set for 2025 but was anchored to a 2023-24 vintage while the private rent target used ONS data from February 2026, understating the social basis by roughly 10% relative to its own target year.

policyengine_uk_data/targets/sources/housing.py

@@ -2,12 +2,24 @@
 
 Total mortgage payments, private rent, and social rent.
 
+All three targets are set for 2025 and should be anchored to comparable
+vintages. The social rent basis previously used EHS 2023-24 while the
+private basis used ONS PRHI from February 2026, understating the social
+target by roughly 10% relative to its own year.
+
 Sources:
 - ONS PRHI Feb 2026: UK avg private rent £1,374/month
   https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/privaterentandhousepricesuk/march2026
-- English Housing Survey 2023-24: avg social rent £118/week
-  https://www.gov.uk/government/statistics/english-housing-survey-2023-to-2024-rented-sectors
+- English Housing Survey 2024-25: avg social rent £129/week (local authority
+  £120, housing association £134)
+  https://www.gov.uk/government/statistics/chapters-for-english-housing-survey-2024-to-2025-headline-findings-on-demographics-and-household-resilience/chapter-2-housing-costs-and-affordability
 - EHS + devolved stats: ~5.4m private renters, ~5.0m social renters UK-wide
+
+Known limitation: these are totals only, so an error in the household count
+and an offsetting error in the mean cannot be detected. At the 1.40.3
+dataset the private target is met (1.04x) with 6.99m renters at £256/week
+against a basis of 5.4m at £317/week — the total matches by cancellation.
+See PolicyEngine/policyengine-uk-data#454.
 """
 
 from policyengine_uk_data.targets.schema import Target, Unit
@@ -18,12 +30,17 @@
 # Mortgage: avg £1,100/month × 7.5m owner-occupiers with mortgage
 _MORTGAGE_TOTAL = 1_100 * 12 * 7.5e6  # ~£99bn
 
-# Social rent: EHS 2023-24 mean £118/week × 52 × 5.0m UK social renters
-_SOCIAL_RENT_TOTAL = 118 * 52 * 5.0e6  # ~£30.7bn
+# Social rent basis, kept as named components so the arithmetic is auditable
+# and the vintage is explicit rather than buried in a product.
+_SOCIAL_RENT_WEEKLY_MEAN = 129  # EHS 2024-25 (was 118 in EHS 2023-24)
+_SOCIAL_RENT_HOUSEHOLDS = 5.0e6  # UK, derived: share x ONS household total
+_SOCIAL_RENT_TOTAL = _SOCIAL_RENT_WEEKLY_MEAN * 52 * _SOCIAL_RENT_HOUSEHOLDS
 
 _EHS_REF = (
     "https://www.gov.uk/government/statistics/"
-    "english-housing-survey-2023-to-2024-rented-sectors"
+    "chapters-for-english-housing-survey-2024-to-2025-headline-findings-on-"
+    "demographics-and-household-resilience/chapter-2-housing-costs-and-"
+    "affordability"
 )
 _ONS_RENT_REF = (
     "https://www.ons.gov.uk/economy/inflationandpriceindices/"

policyengine_uk_data/tests/test_housing_targets.py

@@ -5,6 +5,8 @@
 
 from policyengine_uk_data.targets.sources.housing import (
     _MORTGAGE_TOTAL,
+    _SOCIAL_RENT_HOUSEHOLDS,
+    _SOCIAL_RENT_WEEKLY_MEAN,
     _PRIVATE_RENT_TOTAL,
     _SOCIAL_RENT_TOTAL,
     get_targets,
@@ -20,10 +22,23 @@ def test_private_rent_total_in_range():
 
 
 def test_social_rent_total_in_range():
-    """Social rent total should be £20bn-£40bn (5.0m × ~£118/wk)."""
+    """Social rent total should be £20bn-£40bn (5.0m × ~£129/wk)."""
     assert 20e9 < _SOCIAL_RENT_TOTAL < 40e9
 
 
+def test_social_rent_basis_components():
+    """Pin the documented EHS basis so a silent edit is visible in review.
+
+    This does NOT detect a newer EHS release — it only fails if someone
+    changes the constant without changing this pin. A real staleness check
+    would have to fetch EHS, as ons_tenure.py and ons_households.py do for
+    their sources. Tracked as future work in the module docstring.
+    """
+    assert _SOCIAL_RENT_WEEKLY_MEAN == 129  # EHS 2024-25
+    assert _SOCIAL_RENT_HOUSEHOLDS == 5.0e6
+    assert _SOCIAL_RENT_TOTAL == 129 * 52 * 5.0e6
+
+
 def test_mortgage_total_in_range():
     """Mortgage total should be £80bn-£120bn (7.5m × ~£1,100/mo)."""
     assert 80e9 < _MORTGAGE_TOTAL < 120e9