PyFixest 0.10.8: More flexible DID2s support

.gitignore

@@ -10,4 +10,8 @@ dist
 .pytest_cache
 .vscode
 *.pyc
-__pycache__/
+__pycache__/
+figures
+docs/figures
+docs/news_files
+readme_files

docs/news.md

@@ -1,5 +1,45 @@
 # News
 
+## PyFixest `0.10.8`
+
+### Breaking changes
+Reference levels for the `i()` formula syntax can no longer be set within the formula, but need to be added via the `i_ref1` function argument to either `feols()` and `fepois()`.
+
+### New feature
+
+A `dids2()` function is added, which implements the 2-stage difference-in-differences procedure à la Gardner and follows the syntax of @kylebutts [did2s](https://github.com/kylebutts/did2s) R package.
+
+```py
+from pyfixest.experimental.did import did2s
+from pyfixest.estimation import feols
+from pyfixest.visualize import iplot
+import pandas as pd
+import numpy as np
+
+df_het = pd.read_csv("https://raw.githubusercontent.com/s3alfisc/pyfixest/master/pyfixest/experimental/data/df_het.csv")
+
+fit = did2s(
+    df_het,
+    yname = "dep_var",
+    first_stage = "~ 0 | state + year",
+    second_stage = "~i(rel_year)",
+    treatment = "treat",
+    cluster = "state",
+    i_ref1 = [-1.0, np.inf],
+)
+
+fit_twfe = feols(
+    "dep_var ~ i(rel_year) | state + year",
+    df_het,
+    i_ref1 = [-1.0, np.inf]
+)
+
+iplot([fit, fit_twfe], coord_flip=False, figsize = (900, 400), title = "TWFE vs DID2S")
+```
+![](figures/event_study.svg)
+
+
+
 ## PyFixest `0.10.7`
 
 - Adds basic support for event study estimation via two-way fixed effects and Gardner's two-stage "Did2s" approach.