From 5a2ce0f2f9975cf19778bc9afd36754cb744d720 Mon Sep 17 00:00:00 2001
From: Nikhil Woodruff <35577657+nikhilwoodruff@users.noreply.github.com>
Date: Thu, 17 Oct 2024 23:03:03 +0100
Subject: [PATCH] Make employee incidence a percentage (#964)

* Bump UK data

* Add employee incidence parameter

* Versioning
---
 CHANGELOG.md                                          |  7 +++++++
 changelog.yaml                                        |  5 +++++
 .../policyengine/employer_ni/employee_incidence.yaml  |  6 +++---
 policyengine_uk/reforms/policyengine/budget_change.py |  2 +-
 .../employer_ni_fixed_employer_cost_change.py         | 11 ++++++++---
 setup.py                                              |  2 +-
 6 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 297837c1f..8d84f796d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), 
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.4.0] - 2024-10-17 21:43:42
+
+### Added
+
+- Employee incidence percentage for employer NICs.
+
 ## [2.3.0] - 2024-10-17 10:47:06
 
 ### Changed
@@ -1500,6 +1506,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+[2.4.0]: https://github.com/PolicyEngine/openfisca-uk/compare/2.3.0...2.4.0
 [2.3.0]: https://github.com/PolicyEngine/openfisca-uk/compare/2.2.0...2.3.0
 [2.2.0]: https://github.com/PolicyEngine/openfisca-uk/compare/2.1.1...2.2.0
 [2.1.1]: https://github.com/PolicyEngine/openfisca-uk/compare/2.1.0...2.1.1
diff --git a/changelog.yaml b/changelog.yaml
index 847991412..2c47ea1d3 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -1259,3 +1259,8 @@
     changed:
     - UK-data bumped to 1.5.
   date: 2024-10-17 10:47:06
+- bump: minor
+  changes:
+    added:
+    - Employee incidence percentage for employer NICs.
+  date: 2024-10-17 21:43:42
diff --git a/policyengine_uk/parameters/gov/contrib/policyengine/employer_ni/employee_incidence.yaml b/policyengine_uk/parameters/gov/contrib/policyengine/employer_ni/employee_incidence.yaml
index eebcf37df..e31153a34 100644
--- a/policyengine_uk/parameters/gov/contrib/policyengine/employer_ni/employee_incidence.yaml
+++ b/policyengine_uk/parameters/gov/contrib/policyengine/employer_ni/employee_incidence.yaml
@@ -1,6 +1,6 @@
-description: Assume that employers keep employment costs constant in response to employer NI changes.
+description: Fraction of employer NI that is borne by employees. The remaining is passed onto prices.
 values:
-  2010-01-01: true
+  2010-01-01: 1
 metadata:
   label: Employer NI employee incidence
-  unit: bool
+  unit: /1
diff --git a/policyengine_uk/reforms/policyengine/budget_change.py b/policyengine_uk/reforms/policyengine/budget_change.py
index 6d0b3a04f..ab04edacb 100644
--- a/policyengine_uk/reforms/policyengine/budget_change.py
+++ b/policyengine_uk/reforms/policyengine/budget_change.py
@@ -86,7 +86,7 @@ class pre_budget_change_household_tax(Variable):
         "expected_sdlt",
         "expected_ltt",
         "expected_lbtt",
-        "corporate_sdlt_",
+        "corporate_sdlt",
         "business_rates",
         "council_tax",
         "domestic_rates",
diff --git a/policyengine_uk/variables/contrib/policyengine/employer_ni/employer_ni_fixed_employer_cost_change.py b/policyengine_uk/variables/contrib/policyengine/employer_ni/employer_ni_fixed_employer_cost_change.py
index 039384f7a..53d57560c 100644
--- a/policyengine_uk/variables/contrib/policyengine/employer_ni/employer_ni_fixed_employer_cost_change.py
+++ b/policyengine_uk/variables/contrib/policyengine/employer_ni/employer_ni_fixed_employer_cost_change.py
@@ -22,9 +22,10 @@ class employer_ni_fixed_employer_cost_change(Variable):
     unit = GBP
 
     def formula(person, period, parameters):
-        if not parameters(
+        employee_incidence = parameters(
             period
-        ).gov.contrib.policyengine.employer_ni.employee_incidence:
+        ).gov.contrib.policyengine.employer_ni.employee_incidence
+        if employee_incidence == 0:
             return 0
         # First, calculate baseline and reformed employer NI contributions.
 
@@ -103,8 +104,12 @@ def formula(person, period, parameters):
 
         pay_change = new_employment_income - previous_employment_income
 
+        # Apply incidence percentage
+
+        interpolated_pay_change = pay_change * employee_incidence
+
         # Where a person's prior employment income was below the secondary threshold, the formula doesn't hold, so assume no change.
 
         below_threshold = previous_employment_income < t_b
 
-        return where(below_threshold, 0, pay_change)
+        return where(below_threshold, 0, interpolated_pay_change)
diff --git a/setup.py b/setup.py
index 3c015ee12..897415239 100644
--- a/setup.py
+++ b/setup.py
@@ -4,7 +4,7 @@
 
 setup(
     name="PolicyEngine-UK",
-    version="2.3.0",
+    version="2.4.0",
     author="PolicyEngine",
     author_email="nikhil@policyengine.org",
     classifiers=[