From cf71da1df33f19439d7f588718fafdcb445d5c53 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Thu, 15 Jan 2026 11:45:23 +0000
Subject: [PATCH] Prepare v2.0.2 release: SE accuracy improvements

Update version to 2.0.2 and document the CallawaySantAnna SE
computation fix that now exactly matches R's did package.

The weight influence function (wif) formula was corrected to use
n_g / n_all for pg computation and iterate over keepers with
individual ATT(g,t) values, reducing SE difference from ~2.5%
to <0.01% vs R.
---
 CHANGELOG.md          | 11 +++++++++++
 diff_diff/__init__.py |  2 +-
 pyproject.toml        |  2 +-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 872c482..fa0672e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.0.2] - 2026-01-15
+
+### Fixed
+- **CallawaySantAnna SE computation** now exactly matches R's `did` package
+  - Fixed weight influence function (wif) formula for "simple" aggregation
+  - Corrected `pg` computation: uses `n_g / n_all` (matching R) instead of `n_g / total_treated`
+  - Fixed wif iteration: iterates over keepers (post-treatment pairs) with individual ATT(g,t) values
+  - SE difference reduced from ~2.5% to <0.01% vs R's `did` package (essentially exact match)
+  - Point estimates unchanged; all existing tests pass
+
 ## [2.0.1] - 2026-01-13
 
 ### Added
@@ -358,6 +368,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - `to_dict()` and `to_dataframe()` export methods
   - `is_significant` and `significance_stars` properties
 
+[2.0.2]: https://github.com/igerber/diff-diff/compare/v2.0.1...v2.0.2
 [2.0.1]: https://github.com/igerber/diff-diff/compare/v2.0.0...v2.0.1
 [2.0.0]: https://github.com/igerber/diff-diff/compare/v1.4.0...v2.0.0
 [1.4.0]: https://github.com/igerber/diff-diff/compare/v1.3.1...v1.4.0
diff --git a/diff_diff/__init__.py b/diff_diff/__init__.py
index ba5ef51..920891d 100644
--- a/diff_diff/__init__.py
+++ b/diff_diff/__init__.py
@@ -113,7 +113,7 @@
     plot_sensitivity,
 )
 
-__version__ = "2.0.1"
+__version__ = "2.0.2"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",
diff --git a/pyproject.toml b/pyproject.toml
index 6ab44de..53702f0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "2.0.1"
+version = "2.0.2"
 description = "A library for Difference-in-Differences causal inference analysis"
 readme = "README.md"
 license = "MIT"