diff_diff.placebo_group_test#
- diff_diff.placebo_group_test(data, outcome, time, unit, fake_treated_units, post_periods=None, alpha=0.05, **estimator_kwargs)[source]
Test for differential trends among never-treated units.
Assigns some never-treated units as “fake treated” and estimates a DiD model using only never-treated data. A significant effect suggests heterogeneous trends in the control group.
- Parameters:
data (pd.DataFrame) – Panel data.
outcome (str) – Outcome variable column.
time (str) – Time period column.
unit (str) – Unit identifier column.
fake_treated_units (list) – List of control unit IDs to designate as “fake treated”.
post_periods (list, optional) – List of post-treatment period values.
alpha (float, default=0.05) – Significance level.
**estimator_kwargs – Arguments passed to DifferenceInDifferences.
- Returns:
Results of the fake group placebo test.
- Return type: