Improve growthfactor utils, fix uprating bugs (#1170)

* Fix Enable backwards growth factor application #1169

* Fix Uprate non-labour income sources with nominal GDP growth #1172

* Format

* Update end year

* Reduce end date

Author: nikhilwoodruff

docs/book/assumptions/growthfactors.ipynb

@@ -3,7 +3,7 @@
 from policyengine_uk.data.dataset_schema import UKDataset
 
 START_YEAR = 2020
-END_YEAR = 2034
+END_YEAR = 2029
 
 
 def create_policyengine_uprating_factors_table():
@@ -45,27 +45,45 @@ def create_policyengine_uprating_factors_table():
 
     file_path = Path(__file__).parent / "uprating_growth_factors.csv"
     df_growth["Parameter"] = df.index.map(parameter_by_variable)
+    df_growth = df_growth[
+        ["Parameter"] + [year for year in range(START_YEAR, END_YEAR + 1)]
+    ]
     df_growth.to_csv(file_path)
     return pd.read_csv(file_path)
 
 
+def convert_yoy_growth_to_index(
+    growth_factors: pd.DataFrame,
+):
+    """
+    Convert year-on-year growth factors to an index.
+    """
+    growth_factors = growth_factors.copy()
+    index = growth_factors[growth_factors.columns[2]] * 0 + 1
+    for year in growth_factors.columns[2:]:
+        index *= 1 + growth_factors[year]
+        growth_factors[year] = index
+    return growth_factors
+
+
 def apply_growth_factors(
     dataset: UKDataset,
     growth_factors: pd.DataFrame,
     start_year: int,
     end_year: int,
 ):
+    start_year = str(start_year)
+    end_year = str(end_year)
     dataset = dataset.copy()
+    growth_factors_indices = convert_yoy_growth_to_index(growth_factors)
     for i in range(len(growth_factors)):
-        index = 1
         variable = growth_factors["Variable"].values[i]
-        for year in range(start_year, end_year + 1):
-            growth_factor = growth_factors[str(year)].values[i]
-            index *= 1 + growth_factor
+        start_index = growth_factors_indices[start_year].values[i]
+        end_index = growth_factors_indices[end_year].values[i]
 
         for table in dataset.tables:
             if variable in table.columns:
-                table[variable] *= index
+                table[variable] *= end_index / start_index
 
     return dataset
 

policyengine_uk/data/economic_assumptions.py

@@ -8,6 +8,7 @@
     "gov.obr.employment_income",
     "gov.obr.mixed_income",
     "gov.obr.non_labour_income",
+    "gov.obr.gdp",
 ]
 
 YEARS = list(range(2019, 2035))

policyengine_uk/data/uprating_growth_factors.csv

@@ -0,0 +1,28 @@
+description: OBR forecast for nominal GDP.
+values:
+  2008-01-01: 1582.7
+  2009-01-01: 1558.1
+  2010-01-01: 1627.2
+  2011-01-01: 1672.3
+  2012-01-01: 1727.5
+  2013-01-01: 1800.8
+  2014-01-01: 1879.5
+  2015-01-01: 1931.5
+  2016-01-01: 2015.8
+  2017-01-01: 2099.8
+  2018-01-01: 2170.2
+  2019-01-01: 2240.8
+  2020-01-01: 2085.6
+  2021-01-01: 2357.8
+  2022-01-01: 2583.2
+  2023-01-01: 2749.0
+  2024-01-01: 2881.3
+  2025-01-01: 2993.9
+  2026-01-01: 3101.4
+  2027-01-01: 3219.8
+  2028-01-01: 3339.6
+  2029-01-01: 3464.1
+metadata:
+  reference:
+    - title: OBR March 2025 EFO (detailed forecast tables, economy, table 1.2, column O, fiscal years)
+      href: https://obr.uk/efo/economic-and-fiscal-outlook-march-2025/

policyengine_uk/parameters/gov/obr/add_per_capita_parameters.py

@@ -7,6 +7,5 @@ class afcs(Variable):
     label = "Armed Forces Compensation Scheme"
     definition_period = YEAR
     unit = GBP
-    uprating = "gov.obr.consumer_price_index"
 
     adds = ["afcs_reported"]

policyengine_uk/parameters/gov/obr/gdp.yaml

@@ -27,7 +27,6 @@ class gov_spending(Variable):
         "dla",
         "iidb",
         "incapacity_benefit",
-        "jsa_contrib",
         "pip",
         "sda",
         "state_pension",

policyengine_uk/variables/gov/dwp/afcs.py

@@ -10,4 +10,4 @@ class dividend_income(Variable):
     reference = "Income Tax (Trading and Other Income) Act 2005 s. 365(1)(b-d)"
     unit = GBP
     quantity_type = FLOW
-    uprating = "gov.obr.per_capita.non_labour_income"
+    uprating = "gov.obr.per_capita.gdp"

policyengine_uk/variables/gov/gov_spending.py

@@ -8,4 +8,4 @@ class lump_sum_income(Variable):
     documentation = "Income from lump sums"
     definition_period = YEAR
     unit = GBP
-    uprating = "gov.obr.per_capita.non_labour_income"
+    uprating = "gov.obr.per_capita.gdp"

policyengine_uk/variables/input/dividend_income.py

@@ -8,4 +8,4 @@ class maintenance_income(Variable):
     documentation = "Income from maintenance payments to you"
     definition_period = YEAR
     unit = GBP
-    uprating = "gov.obr.per_capita.non_labour_income"
+    uprating = "gov.obr.per_capita.gdp"