Two data-quality issues surfaced while auditing the geographic results of the council-tax-to-LVT paper (PolicyEngine/uk-lvt-paper). Both materially distort nation-level distributional results.
1. Scottish and Welsh council tax overstated
On enhanced_frs_2023_24.h5@1.55.10 (2026, policyengine-uk 2.88.20), modelled council_tax aggregates by nation:
| Nation |
Model gross |
Model net |
Official comparator |
| England |
£53.8bn |
£50.5bn |
≈£45.6bn requirement 2025–26 (within a few % once uprated to 2026–27) |
| Scotland |
£4.8bn |
£4.0bn |
≈£3.1–3.4bn |
| Wales |
£3.3bn |
£3.1bn |
≈£2.4–2.6bn |
The same pattern holds on enhanced_frs_2024_25.h5 (Scotland £4.3bn gross). Scottish and Welsh liabilities run roughly 20–30% above devolved budget figures while England is close. Average modelled net bill in Scotland (~£1,458) is implausibly near England's (~£1,872) given Scottish band D (~£1,421 in 2024–25, ex-water) and Scotland's band distribution being skewed to A–C. Possible causes worth checking: band-rate averages for Scotland including water/sewerage charges, or the VOA/SAA band calibration weighting.
Downstream effect: any reform crediting households with their abolished council tax (e.g. an LVT swap) overstates Scottish/Welsh gains by £200–300/household/year — enough to flip marginal constituencies from loss to gain.
2. owned_land (WAS direct land holdings) is large and unstable across releases
household_land_value = property_wealth × λ_r + owned_land. The owned_land component:
| Release |
UK total |
Wales avg/hh |
Wales share of Welsh household land |
Scotland share |
| enhanced_frs_2023_24@1.55.10 |
£0.67tn |
£53,548 |
43.6% |
27.6% |
| enhanced_frs_2024_25 (local) |
£0.46tn |
£11,680 |
9.8% |
31.7% |
A 4.6× swing in average Welsh direct landholding between adjacent releases points to a handful of large WAS farm/estate records being imputed into different donors each time. At £0.46–0.67tn this is 9–12% of household land — not noise. Suggest: winsorising the WAS land-value donor variable, imputing it separately from the main wealth block, or at least a regression test on nation-level owned_land aggregates.
Related: PolicyEngine/policyengine-uk#1808 (NI land intensity 0.673). Context: PolicyEngine/uk-lvt-paper#4.
🤖 Generated with Claude Code
Two data-quality issues surfaced while auditing the geographic results of the council-tax-to-LVT paper (PolicyEngine/uk-lvt-paper). Both materially distort nation-level distributional results.
1. Scottish and Welsh council tax overstated
On
enhanced_frs_2023_24.h5@1.55.10(2026, policyengine-uk 2.88.20), modelledcouncil_taxaggregates by nation:The same pattern holds on
enhanced_frs_2024_25.h5(Scotland £4.3bn gross). Scottish and Welsh liabilities run roughly 20–30% above devolved budget figures while England is close. Average modelled net bill in Scotland (~£1,458) is implausibly near England's (~£1,872) given Scottish band D (~£1,421 in 2024–25, ex-water) and Scotland's band distribution being skewed to A–C. Possible causes worth checking: band-rate averages for Scotland including water/sewerage charges, or the VOA/SAA band calibration weighting.Downstream effect: any reform crediting households with their abolished council tax (e.g. an LVT swap) overstates Scottish/Welsh gains by £200–300/household/year — enough to flip marginal constituencies from loss to gain.
2.
owned_land(WAS direct land holdings) is large and unstable across releaseshousehold_land_value = property_wealth × λ_r + owned_land. Theowned_landcomponent:A 4.6× swing in average Welsh direct landholding between adjacent releases points to a handful of large WAS farm/estate records being imputed into different donors each time. At £0.46–0.67tn this is 9–12% of household land — not noise. Suggest: winsorising the WAS land-value donor variable, imputing it separately from the main wealth block, or at least a regression test on nation-level
owned_landaggregates.Related: PolicyEngine/policyengine-uk#1808 (NI land intensity 0.673). Context: PolicyEngine/uk-lvt-paper#4.
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