Mirror PR #405's docstring CV notation into summary labels + bacon param block

PR #405 changed coef_var docstrings from "SE / |ATT|" to "SE / abs(ATT)"
to avoid Sphinx interpreting |...| as a substitution reference, but did
not mirror the same change into the user-facing summary labels rendered
by summary() / print(). The result: docstrings now describe the metric
as "SE/abs(ATT)" while the terminal prints "CV (SE/|ATT|):" — two
labels for the same quantity.

Mirror the notation across all 14 summary call sites and update the
single cached T18 tutorial output that quotes the label:

- diff_diff/results.py (3 sites: DiD/MultiPeriod/SyntheticDiD)
- diff_diff/{continuous_did,efficient_did,imputation,stacked_did,
  staggered,staggered_triple_diff,trop,two_stage}_results.py (1 each)
- diff_diff/sun_abraham.py (1)
- diff_diff/chaisemartin_dhaultfoeuille_results.py (dynamic
  f"CV (SE/|{label}|):" -> f"CV (SE/abs({label})):")
- docs/tutorials/18_geo_experiments.ipynb (1 cached output line)

Also mirror PR #405's blank-line-before-bullet-list fix into
BaconDecomposition.__init__ at bacon.py:404, matching the same fix
already applied to bacon_decompose() at bacon.py:1086 and 1097 by
PR #405. This Parameters block is rendered through
docs/api/_autosummary/diff_diff.BaconDecomposition.rst.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: igerber

diff_diff/bacon.py

@@ -402,6 +402,7 @@ def __init__(self, weights: str = "approximate"):
         ----------
         weights : str, default="approximate"
             Weight calculation method:
+
             - "approximate": Fast simplified formula (default)
             - "exact": Variance-based weights from Goodman-Bacon (2021)
         """

diff_diff/chaisemartin_dhaultfoeuille_results.py

@@ -893,7 +893,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            cv_label = f"CV (SE/|{overall_row_label}|):"
+            cv_label = f"CV (SE/abs({overall_row_label})):"
             lines.append(f"{cv_label:<25} {cv:>10.4f}")
 
         lines.append("")

diff_diff/continuous_did_results.py

@@ -276,7 +276,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/efficient_did_results.py

@@ -260,7 +260,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/imputation_results.py

@@ -255,7 +255,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/results.py

@@ -249,7 +249,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         # Add significance codes
         lines.extend(
@@ -656,7 +656,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         # Add significance codes
         lines.extend(
@@ -1052,7 +1052,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         # Show top unit weights
         if self.unit_weights:

diff_diff/stacked_did_results.py

@@ -212,7 +212,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/staggered_results.py

@@ -234,7 +234,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/staggered_triple_diff_results.py

@@ -196,7 +196,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")
 

diff_diff/sun_abraham.py

@@ -190,7 +190,7 @@ def summary(self, alpha: Optional[float] = None) -> str:
 
         cv = self.coef_var
         if np.isfinite(cv):
-            lines.append(f"{'CV (SE/|ATT|):':<25} {cv:>10.4f}")
+            lines.append(f"{'CV (SE/abs(ATT)):':<25} {cv:>10.4f}")
 
         lines.append("")