中文摘要
一种强有力的共识认为，劳动所得税抵免（EITC）对劳动供给的广延边际产生了相当大的影响，尤其是对单身母亲而言。本文重新评估了支撑这一共识的双重差分与事件研究方法。本文考察了自该政策实施以来联邦和州层面的每一次EITC改革。所有改革均在事件研究框架下进行分析，并提供了对模型不确定性的全面分析。除1993年的联邦改革外，EITC扩张与就业之间并未表现出任何明确且稳健的效应。约500项事件研究所得的处理效应估计围绕零对称分布。具有较大弹性的设定在该分布中属于离群值。另一方面，1993年的改革与单身母亲就业的大幅增加相关。基于多项不同的分析，本文表明，这些就业增加与福利改革和宏观经济带来的混淆效应更为吻合，而非源于EITC本身。总体而言，关于EITC改革的双重差分和事件研究分析对模型设定选择较为敏感，并不支持存在稳健的较大效应。
Abstract
A strong consensus posits that the Earned Income Tax Credit (EITC) has had sizable effects on extensive margin labor supply, especially for single mothers. This paper reappraises the difference-in-differences and event study approaches that underpin much of this consensus. The paper investigates every EITC reform at the state and federal level since the inception of the policy. All reforms are analyzed in an event study framework and a comprehensive analysis of model uncertainty is presented. Apart from the federal 1993 reform, EITC expansions are not associated with any clear and robust effects on employment. Treatment impact estimates from about 500 event studies are symmetrically distributed around zero. Specifications with large elasticities are outliers in the distribution. The 1993 reform, on the other hand, is associated with large employment increases for single mothers. Based on a number of different analyses, the paper shows that these increases align more closely with confounding effects from welfare reform and the macroeconomy than with the EITC. Overall, difference-in-differences and event study analyses of EITC reforms are fragile to specification choices and do not support robustly large effects.