Eti Bunching Replication

Implements the Saez (2010 AEJ:EP) bunching estimator to identify behavioral responses to marginal tax rates at income kink points. Uses IRS Statistics of Income (SOI) public use microdata. The bunching methodology is a gold standard for estimating the ETI without requiring policy reform experiments. Compares wage earners vs. self-employed — the core result showing self-employed bunch at EITC kinks but wage earners do not.