Add historical Housing Benefit non-dependant deduction rates

changelog.d/hb-nondep-history.fixed.md

@@ -0,0 +1 @@
+- Added the enacted 2015 to 2017 Housing Benefit non-dependant deduction thresholds and amounts instead of backdating the 2018 scale.

policyengine_uk/parameters/gov/dwp/housing_benefit/non_dep_deduction/amount.yaml

@@ -2,73 +2,253 @@ description: The following amount is provided for individuals under the Housing
 
 brackets:
 - threshold:
+    2015-04-01:
+      value: 0
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 0
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 0
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 0
   amount:
+    2015-04-01:
+      value: 14.55
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 14.65
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 14.8
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 15.25
     2021-04-01: 15.95
     2022-04-01: 16.45
     2023-04-01: 18.1
     2024-04-01: 19.3
     2026-04-01: 20.4
 - threshold:
+    2015-04-01:
+      value: 129
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 133
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 136
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 139
     2021-04-01: 154
     2023-04-01: 162
     2024-04-01: 176
     2026-04-01: 192
   amount:
+    2015-04-01:
+      value: 33.4
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 33.65
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 34
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 35
     2021-04-01: 36.65
     2022-04-01: 37.8
     2023-04-01: 41.6
     2024-04-01: 44.4
     2026-04-01: 46.85
 - threshold:
+    2015-04-01:
+      value: 189
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 195
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 200
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 204
     2021-04-01: 224
     2023-04-01: 236
     2024-04-01: 256
     2026-04-01: 279
   amount:
+    2015-04-01:
+      value: 45.85
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 46.2
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 46.65
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 48.05
     2021-04-01: 50.3
     2022-04-01: 51.85
     2023-04-01: 57.1
     2024-04-01: 60.95
     2026-04-01: 64.35
 - threshold:
+    2015-04-01:
+      value: 246
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 253
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 259
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 265
     2021-04-01: 292
     2023-04-01: 308
     2024-04-01: 334
     2026-04-01: 365
   amount:
+    2015-04-01:
+      value: 75.05
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 75.6
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 76.35
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 78.65
     2021-04-01: 82.3
     2022-04-01: 84.85
     2023-04-01: 93.4
     2024-04-01: 99.65
     2026-04-01: 105.2
 - threshold:
+    2015-04-01:
+      value: 328
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 338
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 346
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 354
     2021-04-01: 389
     2023-04-01: 410
     2024-04-01: 445
     2026-04-01: 485
   amount:
+    2015-04-01:
+      value: 85.45
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 86.1
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 86.95
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 89.55
     2021-04-01: 93.7
     2022-04-01: 96.6
     2023-04-01: 106.35
     2024-04-01: 113.5
     2026-04-01: 119.85
 - threshold:
+    2015-04-01:
+      value: 408
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 420
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 430
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 439
     2021-04-01: 484
     2023-04-01: 511
     2024-04-01: 554
     2026-04-01: 605
   amount:
+    2015-04-01:
+      value: 93.8
+      reference:
+        - title: 2015 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2015/457/article/18/made
+    2016-04-01:
+      value: 94.5
+      reference:
+        - title: 2016 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2016/242/regulation/5/made
+    2017-04-01:
+      value: 95.45
+      reference:
+        - title: 2017 Housing Benefit non-dependant deduction uprating
+          href: https://www.legislation.gov.uk/uksi/2017/260/article/22/made
     2018-06-18: 98.3
     2021-04-01: 102.85
     2022-04-01: 106.05

policyengine_uk/tests/test_housing_benefit_non_dep_history.py

@@ -0,0 +1,43 @@
+"""Complete historical HB scale, separate from deduction eligibility rules."""
+
+from pathlib import Path
+
+import numpy as np
+import pytest
+from policyengine_core.parameters.helpers import load_parameter_file
+
+PATH = (
+    Path(__file__).resolve().parents[1]
+    / "parameters/gov/dwp/housing_benefit/non_dep_deduction/amount.yaml"
+)
+
+
+@pytest.mark.parametrize(
+    "year, thresholds, amounts",
+    [
+        (
+            2015,
+            [0, 129, 189, 246, 328, 408],
+            [14.55, 33.40, 45.85, 75.05, 85.45, 93.80],
+        ),
+        (
+            2016,
+            [0, 133, 195, 253, 338, 420],
+            [14.65, 33.65, 46.20, 75.60, 86.10, 94.50],
+        ),
+        (
+            2017,
+            [0, 136, 200, 259, 346, 430],
+            [14.80, 34.00, 46.65, 76.35, 86.95, 95.45],
+        ),
+    ],
+)
+def test_all_historical_scale_cells(year, thresholds, amounts):
+    # SI 2015/457 art 18(3); SI 2016/242 reg 5; SI 2017/260 art 22(4).
+    # Test the parameter itself, not the separate #2007 eligibility/banding fix.
+    scale = load_parameter_file(str(PATH), "hb_non_dep_scale")(f"{year}-04-30")
+    assert scale.thresholds == thresholds
+    assert scale.amounts == amounts
+    np.testing.assert_allclose(
+        scale.calc(np.array(thresholds)), amounts, rtol=0, atol=0
+    )