diff_diff.load_card_krueger#

diff_diff.load_card_krueger(force_download=False)[source]

Load the Card & Krueger (1994) minimum wage dataset.

This classic dataset examines the effect of New Jersey’s 1992 minimum wage increase on employment in fast-food restaurants, using Pennsylvania as a control group.

The study is a canonical example of the Difference-in-Differences method.

Parameters:: force_download (bool, default=False) – If True, re-download the dataset even if cached.
Returns:: Dataset with columns: - store_id : int - Unique store identifier - state : str - ‘NJ’ (New Jersey, treated) or ‘PA’ (Pennsylvania, control) - chain : str - Fast food chain (‘bk’, ‘kfc’, ‘roys’, ‘wendys’) - emp_pre : float - Full-time equivalent employment before (Feb 1992) - emp_post : float - Full-time equivalent employment after (Nov 1992) - wage_pre : float - Starting wage before - wage_post : float - Starting wage after - treated : int - 1 if NJ, 0 if PA - emp_change : float - Change in employment (emp_post - emp_pre)
Return type:: pd.DataFrame

Notes

The minimum wage in New Jersey increased from $4.25 to $5.05 on April 1, 1992. Pennsylvania’s minimum wage remained at $4.25.

Original finding: No significant negative effect of minimum wage increase on employment (ATT ≈ +2.8 FTE employees).

References

Card, D., & Krueger, A. B. (1994). Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania. American Economic Review, 84(4), 772-793.

Examples

>>> from diff_diff.datasets import load_card_krueger
>>> from diff_diff import DifferenceInDifferences
>>>
>>> # Load and prepare data
>>> ck = load_card_krueger()
>>> ck_long = ck.melt(
...     id_vars=['store_id', 'state', 'treated'],
...     value_vars=['emp_pre', 'emp_post'],
...     var_name='period', value_name='employment'
... )
>>> ck_long['post'] = (ck_long['period'] == 'emp_post').astype(int)
>>>
>>> # Estimate DiD
>>> did = DifferenceInDifferences()
>>> results = did.fit(ck_long, outcome='employment', treatment='treated', time='post')