Fix Scottish working-age CTR severe-disability family test

changelog.d/fix-2295-scottish-ctr-nondependants.fixed.md

@@ -0,0 +1 @@
+Use Scotland's working-age Council Tax Reduction young-person definition for the severe disability premium's non-dependant test within the applicant's benefit unit, retaining existing looked-after and other-benefit-unit treatment.

policyengine_uk/tests/policy/baseline/gov/local_authorities/council_tax_reduction/severe_disability_premium_young_person.yaml

@@ -0,0 +1,167 @@
+# SSI2021/249 regs6,8(2)(a),Sch1para13. Existing2026 model controls:
+# allowance95.55*52=4968.60; severe86.05*52=4474.60; withdrawal20%.
+# PIP qualifies SDP but generic disability flag is separately supplied/defaultfalse.
+# Pension12570:no tax; PIP disregarded; Child Benefit claim declined.
+# CTR=2000-20%*(12570-allowance):479.72 or1374.64.
+# Annual UC terminal-date input represents unavailable assessment-period detail.
+# Reverse case supplies CB family status: input-contract composition,
+# not a naturally derived eligibility pair or full statutory rate audit.
+# Shared HB premium component and IS applicable amount are protected below.
+# This household has no continuing HB claim, so its gated HB applicable
+# amount is0; it is not used as a positive HB-payment regression oracle.
+- name: 'Terminal-date input contract: CB young person after UC terminal date removes
+    Scottish CTR premium'
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      applicant:
+        age: 45
+        is_claimant_or_partner: true
+        pip_dl_category: ENHANCED
+        private_pension_income: 12570
+      student:
+        age: 19
+        current_education: UPPER_SECONDARY
+        age_started_or_accepted_current_education_or_training: 17
+        is_before_universal_credit_qualifying_young_person_terminal_date: false
+        is_claimant_or_partner: false
+    benunits:
+      family:
+        members:
+        - applicant
+        - student
+        claims_all_entitled_benefits: true
+        would_claim_uc: false
+        would_claim_IS: false
+        would_claim_pc: false
+        would_claim_CTC: false
+        would_claim_WTC: false
+        would_claim_child_benefit: false
+    households:
+      home:
+        members:
+        - applicant
+        - student
+        country: SCOTLAND
+        local_authority: CITY_OF_EDINBURGH
+        council_tax: 2000
+        savings: 0
+  output:
+    simulated_council_tax_reduction_benunit: 479.72
+    disability_premium: 0
+    enhanced_disability_premium: 0
+    severe_disability_premium: 4474.6
+    council_tax_reduction_pensioner: false
+    council_tax_reduction_applicable_income: 12570
+    council_tax_reduction_applicable_amount: 4968.6
+    council_tax_reduction_non_dep_deductions: 0
+    severe_disability_premium_before_non_dependant_test: 4474.6
+    council_tax_reduction_severe_disability_premium: 0
+    working_age_benefits_premiums: 4474.6
+    benefits_premiums: 4474.6
+    income_support_applicable_amount: 9443.2
+- name: Before terminal date both definitions retain Scottish CTR premium
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      applicant:
+        age: 45
+        is_claimant_or_partner: true
+        pip_dl_category: ENHANCED
+        private_pension_income: 12570
+      student:
+        age: 19
+        current_education: UPPER_SECONDARY
+        age_started_or_accepted_current_education_or_training: 17
+        is_before_universal_credit_qualifying_young_person_terminal_date: true
+        is_claimant_or_partner: false
+    benunits:
+      family:
+        members:
+        - applicant
+        - student
+        claims_all_entitled_benefits: true
+        would_claim_uc: false
+        would_claim_IS: false
+        would_claim_pc: false
+        would_claim_CTC: false
+        would_claim_WTC: false
+        would_claim_child_benefit: false
+    households:
+      home:
+        members:
+        - applicant
+        - student
+        country: SCOTLAND
+        local_authority: CITY_OF_EDINBURGH
+        council_tax: 2000
+        savings: 0
+  output:
+    simulated_council_tax_reduction_benunit: 1374.64
+    disability_premium: 0
+    enhanced_disability_premium: 0
+    severe_disability_premium: 4474.6
+    council_tax_reduction_pensioner: false
+    council_tax_reduction_applicable_income: 12570
+    council_tax_reduction_applicable_amount: 9443.2
+    council_tax_reduction_non_dep_deductions: 0
+    severe_disability_premium_before_non_dependant_test: 4474.6
+    council_tax_reduction_severe_disability_premium: 4474.6
+    working_age_benefits_premiums: 4474.6
+    benefits_premiums: 4474.6
+    income_support_applicable_amount: 9443.2
+- name: 'Supplied-status contract: UC young person outside CB family restores Scottish
+    CTR premium'
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      applicant:
+        age: 45
+        is_claimant_or_partner: true
+        pip_dl_category: ENHANCED
+        private_pension_income: 12570
+      student:
+        age: 19
+        current_education: UPPER_SECONDARY
+        age_started_or_accepted_current_education_or_training: 17
+        is_before_universal_credit_qualifying_young_person_terminal_date: true
+        is_claimant_or_partner: false
+        is_child_or_qualifying_young_person_for_child_benefit: false
+    benunits:
+      family:
+        members:
+        - applicant
+        - student
+        claims_all_entitled_benefits: true
+        would_claim_uc: false
+        would_claim_IS: false
+        would_claim_pc: false
+        would_claim_CTC: false
+        would_claim_WTC: false
+        would_claim_child_benefit: false
+    households:
+      home:
+        members:
+        - applicant
+        - student
+        country: SCOTLAND
+        local_authority: CITY_OF_EDINBURGH
+        council_tax: 2000
+        savings: 0
+  output:
+    simulated_council_tax_reduction_benunit: 1374.64
+    disability_premium: 0
+    enhanced_disability_premium: 0
+    severe_disability_premium: 0
+    council_tax_reduction_pensioner: false
+    council_tax_reduction_applicable_income: 12570
+    council_tax_reduction_applicable_amount: 9443.2
+    council_tax_reduction_non_dep_deductions: 0
+    severe_disability_premium_before_non_dependant_test: 4474.6
+    council_tax_reduction_severe_disability_premium: 4474.6
+    working_age_benefits_premiums: 0
+    benefits_premiums: 0
+    income_support_applicable_amount: 4968.6

policyengine_uk/tests/test_council_tax_reduction_severe_disability_family.py

@@ -0,0 +1,141 @@
+"""CTR family-mask input contracts, separate from derived eligibility tests.
+
+SSI 2021/249 regs 6 and 8(2)(a), Sch 1 para 13 retain an applicant's
+UC young person in their family. These finite grids deliberately supply the
+two young-person statuses to exercise both directions independently of the
+upstream eligibility rules. The policy YAML uses school/course inputs and
+the annual terminal-date input, plus actual PIP, pension and council tax.
+
+Looked-after and other-benefit-unit treatment remains the existing model
+baseline, not a certification of reg 8(2)(b) and its paragraph (3) overrides.
+"""
+
+from itertools import product
+
+import numpy as np
+import pytest
+
+from policyengine_uk import Simulation
+
+
+def input_grid(rows, country="SCOTLAND", year=2026, applicant_age=45):
+    people, benunits, households = {}, {}, {}
+    for i, row in enumerate(rows):
+        applicant, student = f"a{i}", f"s{i}"
+        people[applicant] = {
+            "age": applicant_age,
+            "is_claimant_or_partner": True,
+            "pip_dl_category": "ENHANCED",
+        }
+        people[student] = {
+            "age": row.get("age", 19),
+            "is_claimant_or_partner": False,
+            "is_child_or_qualifying_young_person_for_child_benefit": row["cb"],
+            "is_qualifying_young_person_for_universal_credit": row["uc"],
+            "is_looked_after_by_local_authority": row.get("looked_after", False),
+            "is_blind": row.get("blind", False),
+            "pip_dl_category": "STANDARD" if row.get("benefit", False) else "NONE",
+        }
+        members = [applicant, student]
+        benunits[f"b{i}"] = {
+            "members": [applicant] if row.get("other_bu", False) else members,
+            "would_claim_uc": False,
+            "would_claim_IS": False,
+            "would_claim_pc": False,
+        }
+        if row.get("other_bu", False):
+            benunits[f"other{i}"] = {"members": [student]}
+        households[f"h{i}"] = {"members": members, "country": country}
+    situation = {"people": people, "benunits": benunits, "households": households}
+    # A situation's default period is the model default, not necessarily year.
+    for group in situation.values():
+        for values in group.values():
+            for name, value in list(values.items()):
+                if name != "members":
+                    values[name] = {year: value}
+    return Simulation(situation=situation), [f"b{i}" for i in range(len(rows))]
+
+
+def values(sim, variable, names, year=2026):
+    result = sim.calculate(variable, year)
+    ids = list(sim.populations["benunit"].ids)
+    return np.array([result[ids.index(name)] for name in names])
+
+
+@pytest.mark.parametrize(
+    "country,year,applicant_age,scottish_working_age",
+    [
+        ("SCOTLAND", 2026, 45, True),
+        ("SCOTLAND", 2021, 45, False),
+        ("SCOTLAND", 2026, 70, False),
+        ("ENGLAND", 2026, 45, False),
+        ("WALES", 2026, 45, False),
+        ("NORTHERN_IRELAND", 2026, 45, False),
+    ],
+)
+def test_own_family_status_contract_by_applicant_scheme(
+    country, year, applicant_age, scottish_working_age
+):
+    rows = [
+        dict(cb=cb, uc=uc, looked_after=looked_after)
+        for cb, uc, looked_after in product([False, True], repeat=3)
+    ]
+    sim, names = input_grid(rows, country, year, applicant_age)
+    expected = [
+        not (
+            row["uc"] if scottish_working_age and not row["looked_after"] else row["cb"]
+        )
+        for row in rows
+    ]
+    assert (
+        values(
+            sim,
+            "has_non_dependant_for_council_tax_reduction_severe_disability_premium",
+            names,
+            year,
+        ).tolist()
+        == expected
+    )
+    # HB and IS retain the original Child Benefit family classification.
+    assert values(
+        sim, "has_non_dependant_for_severe_disability_premium", names, year
+    ).tolist() == [not row["cb"] for row in rows]
+
+
+def test_age_boundary_and_blind_or_benefit_exceptions():
+    rows = [
+        dict(age=age, cb=True, uc=False, blind=blind, benefit=benefit)
+        for age, blind, benefit in product(
+            [17.999, 18, 19, 20], [False, True], [False, True]
+        )
+    ]
+    sim, names = input_grid(rows)
+    expected = [
+        row["age"] >= 18 and not row["blind"] and not row["benefit"] for row in rows
+    ]
+    assert (
+        values(
+            sim,
+            "has_non_dependant_for_council_tax_reduction_severe_disability_premium",
+            names,
+        ).tolist()
+        == expected
+    )
+    # The shared gate still disregards these own-BU Child Benefit young people.
+    assert not values(
+        sim, "has_non_dependant_for_severe_disability_premium", names
+    ).any()
+
+
+def test_other_benefit_units_keep_existing_treatment():
+    rows = [
+        dict(cb=cb, uc=uc, looked_after=looked_after, other_bu=True)
+        for cb, uc, looked_after in product([False, True], repeat=3)
+    ]
+    sim, names = input_grid(rows)
+    assert values(sim, "has_non_dependant_for_severe_disability_premium", names).all()
+    assert values(
+        sim,
+        "has_non_dependant_for_council_tax_reduction_severe_disability_premium",
+        names,
+    ).all()

policyengine_uk/variables/gov/local_authorities/council_tax_reduction/council_tax_reduction_applicable_amount.py

@@ -57,6 +57,10 @@ def formula(benunit, period, parameters):
         premiums = where(
             pensioner,
             benunit("pension_age_benefits_premiums", period),
-            benunit("working_age_benefits_premiums", period),
+            benunit("working_age_benefits_premiums", period)
+            + (
+                benunit("council_tax_reduction_severe_disability_premium", period)
+                - benunit("severe_disability_premium", period)
+            ),
         )
         return personal_allowance + premiums

policyengine_uk/variables/gov/local_authorities/council_tax_reduction/council_tax_reduction_severe_disability_premium.py

@@ -0,0 +1,30 @@
+from policyengine_uk.model_api import *
+
+
+class council_tax_reduction_severe_disability_premium(Variable):
+    value_type = float
+    entity = BenUnit
+    label = "Working-age CTR severe disability premium"
+    documentation = (
+        "The shared legacy premium's amount before its non-dependant test, "
+        "with the Council Tax Reduction-specific family test applied. This "
+        "allows either direction of a difference between the Universal Credit "
+        "and Child Benefit young-person definitions. The test retains the "
+        "existing classification for looked-after residents and other benefit "
+        "units; see has_non_dependant_for_council_tax_reduction_severe_disability_premium. "
+        "Pension-age Council Tax Reduction continues to use its separate premium."
+    )
+    definition_period = YEAR
+    unit = GBP
+    reference = (
+        "https://www.legislation.gov.uk/ssi/2021/249/regulation/8",
+        "https://www.legislation.gov.uk/ssi/2021/249/schedule/1/paragraph/13",
+    )
+
+    def formula(benunit, period, parameters):
+        amount = benunit("severe_disability_premium_before_non_dependant_test", period)
+        no_non_dependant = ~benunit(
+            "has_non_dependant_for_council_tax_reduction_severe_disability_premium",
+            period,
+        )
+        return amount * no_non_dependant