diff_diff.check_parallel_trends

diff_diff.check_parallel_trends(data, outcome, time, treatment_group, pre_periods=None)

Perform a simple check for parallel trends assumption.

This computes the trend (slope) in the outcome variable for both treatment and control groups during pre-treatment periods.

Parameters:

• data (pd.DataFrame) – Panel data.

• outcome (str) – Name of outcome variable column.

• time (str) – Name of time period column.

• treatment_group (str) – Name of treatment group indicator column.

• pre_periods (list, optional) – List of pre-treatment time periods. If None, infers from data.

Returns:

Dictionary with trend statistics and test results.

Return type:

dict