Fix UC higher disabled-child eligibility

changelog.d/1970.fixed.md

@@ -0,0 +1 @@
+- Separated Universal Credit's higher disabled child condition from tax credits, included certified blindness, and prevented the lower and higher additions from stacking.

policyengine_uk/parameters/gov/dwp/universal_credit/elements/child/severely_disabled/benefit_amount_tolerance.yaml

@@ -0,0 +1,10 @@
+description: Weekly tolerance for the modeled paid-amount proxy for qualifying DLA care and PIP daily living awards in the Universal Credit higher disabled child condition. This is an existing input approximation, not a statutory entitlement threshold.
+values:
+  2015-01-01: 10
+metadata:
+  unit: currency-GBP
+  period: week
+  label: UC higher disabled child benefit amount proxy tolerance
+  reference:
+    - title: Retained PolicyEngine-UK DLA and PIP paid-amount input convention
+      href: https://github.com/PolicyEngine/policyengine-uk/blob/b4dbaf57a4ebb1d1f0ba5f7a384795422828db75/policyengine_uk/variables/household/demographic/is_severely_disabled_for_benefits.py

policyengine_uk/tests/policy/baseline/finance/benefit/family/universal_credit/child_element/disability/uc_individual_severely_disabled_child_element.yaml

@@ -4,7 +4,7 @@
   input:
     age: 6
     is_uc_claimant: false
-    is_severely_disabled_for_benefits: true
+    dla_sc_category: HIGHER
   output:
     uc_individual_severely_disabled_child_element: 5_942
 
@@ -14,7 +14,7 @@
   input:
     age: 18
     is_in_non_advanced_education: true
-    is_severely_disabled_for_benefits: true
+    dla_sc_category: HIGHER
   output:
     is_uc_claimant: true
     uc_individual_severely_disabled_child_element: 0

policyengine_uk/tests/policy/baseline/finance/benefit/family/universal_credit/claimant_child_element.yaml

@@ -115,7 +115,7 @@
         is_disabled_for_benefits: true
       person5:
         age: 2
-        is_severely_disabled_for_benefits: true
+        dla_sc_category: HIGHER
     benunits:
       benunit:
         members: [person1, person2, person3, person4, person5]

policyengine_uk/tests/policy/integration/uc_disabled_child_addition.yaml

@@ -0,0 +1,202 @@
+# Classification: UC Regs 2013 reg 24(2), with the existing statutory-blind
+# input. Cash anchors are the unchanged model's 2026 monthly amounts:
+# standard 424.90, ordinary child 303.94, lower 164.79, higher 514.71.
+# A parent with a post-April-2017 child and no recovered debt therefore gets
+# 12 * (424.90 + 303.94 + the single applicable disability addition).
+# Only blind/no-award cases assert final UC: the existing generic disability
+# flag also defaults LCWRA for child members, a separate model approximation.
+
+- name: A certified blind dependent receives the higher UC child addition without a disability benefit
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+        is_blind: true
+    benunits:
+      family:
+        members: [parent, child]
+        uc_has_deduction: false
+    households:
+      home:
+        members: [parent, child]
+        region: LONDON
+  output:
+    uc_individual_disabled_child_element: [0, 0]
+    uc_individual_severely_disabled_child_element: [0, 6_176.52]
+    uc_disability_elements: 6_176.52
+    universal_credit: 14_922.60
+
+- name: Blindness and highest DLA care give one higher addition rather than both tiers
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+        is_blind: true
+        dla_sc_category: HIGHER
+        is_disabled_for_benefits: true
+    benunits:
+      family:
+        members: [parent, child]
+        uc_has_deduction: false
+    households:
+      home:
+        members: [parent, child]
+        region: LONDON
+  output:
+    uc_individual_disabled_child_element: [0, 0]
+    uc_individual_severely_disabled_child_element: [0, 6_176.52]
+
+- name: Middle DLA care retains only the lower disabled child addition
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+        dla_sc_category: MIDDLE
+        is_disabled_for_benefits: true
+    benunits:
+      family:
+        members: [parent, child]
+        uc_has_deduction: false
+    households:
+      home:
+        members: [parent, child]
+        region: LONDON
+  output:
+    uc_individual_disabled_child_element: [0, 1_977.48]
+    uc_individual_severely_disabled_child_element: [0, 0]
+
+- name: A nonblind child without a qualifying award receives no disability addition
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+    benunits:
+      family:
+        members: [parent, child]
+        uc_has_deduction: false
+    households:
+      home:
+        members: [parent, child]
+        region: LONDON
+  output:
+    uc_individual_disabled_child_element: [0, 0]
+    uc_individual_severely_disabled_child_element: [0, 0]
+    universal_credit: 8_746.08
+
+- name: An enhanced PIP daily living qualifying young person receives only the higher addition
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 45
+        is_parent: true
+        is_benunit_head: true
+      young_person:
+        age: 18
+        is_benunit_head: false
+        is_in_non_advanced_education: true
+        age_started_or_accepted_current_education_or_training: 17
+        pip_dl_category: ENHANCED
+        is_disabled_for_benefits: true
+    benunits:
+      family:
+        members: [parent, young_person]
+    households:
+      home:
+        members: [parent, young_person]
+  output:
+    is_uc_claimant: [true, false]
+    uc_individual_disabled_child_element: [0, 0]
+    uc_individual_severely_disabled_child_element: [0, 6_176.52]
+
+- name: A blind young claimant does not receive a child addition for themselves
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    age: 18
+    is_in_non_advanced_education: true
+    is_blind: true
+    is_disabled_for_benefits: true
+  output:
+    is_uc_claimant: true
+    uc_individual_disabled_child_element: 0
+    uc_individual_severely_disabled_child_element: 0
+
+- name: A blind outside adult does not create a child addition for another family
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+      outside_adult:
+        age: 30
+        is_blind: true
+    benunits:
+      family:
+        members: [parent, child]
+      other_family:
+        members: [outside_adult]
+    households:
+      home:
+        members: [parent, child, outside_adult]
+  output:
+    uc_individual_disabled_child_element: [0, 0, 0]
+    uc_individual_severely_disabled_child_element: [0, 0, 0]
+
+- name: A stored tax credit severe flag alone is not evidence of the UC higher condition
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      parent:
+        age: 35
+        is_parent: true
+        is_benunit_head: true
+      child:
+        age: 8
+        is_benunit_head: false
+        is_severely_disabled_for_benefits: true
+    benunits:
+      family:
+        members: [parent, child]
+    households:
+      home:
+        members: [parent, child]
+  output:
+    uc_individual_disabled_child_element: [0, 0]
+    uc_individual_severely_disabled_child_element: [0, 0]