We introduce a new nonparametric causal decomposition approach that identifies the mechanisms by which a treatment variable contributes to a group-based outcome disparity. Our approach distinguishes three mechanisms: group differences in 1) treatment prevalence, 2) average treatment effects, and 3) selection into treatment based on individual-level treatment effects. Our approach reformulates classic Kitagawa-Blinder-Oaxaca decompositions in causal and nonparametric terms, complements causal mediation analysis by explaining group disparities instead of group effects, and isolates conceptually distinct mechanisms conflated in recent random equalization decompositions. In contrast to all prior approaches, our framework uniquely identifies differential selection into treatment as a novel disparity-generating mechanism. Our approach can be used for both the retrospective causal explanation of disparities and the prospective planning of interventions to change disparities. We present both an unconditional and a conditional decomposition, where the latter quantifies the contributions of the treatment within levels of certain covariates. We develop nonparametric estimators that are $\sqrt{n}$-consistent, asymptotically normal, semiparametrically efficient, and multiply robust. We apply our approach to analyze the mechanisms by which college graduation causally contributes to intergenerational income persistence (the disparity in adult income between the children of high- vs low-income parents). Empirically, we demonstrate a previously undiscovered role played by the new selection component in intergenerational income persistence.

翻译：我们提出了一种新的非参数因果分解方法，用于识别处理变量如何通过特定机制导致基于群体的结果差异。该方法区分了三种机制：1) 处理发生率的群体差异，2) 平均处理效应的群体差异，以及3) 基于个体层面处理效应的处理选择差异。我们的研究将经典的Kitagawa-Blinder-Oaxaca分解重新表述为因果与非参数形式，通过解释群体差异而非群体效应来补充因果中介分析，并分离了近期随机均衡分解中混淆的概念上不同的机制。与所有先前方法相比，我们的框架首次将差异化的处理选择识别为一种新的差异生成机制。该方法既可用于差异的回顾性因果解释，也可用于改变差异的干预措施前瞻性规划。我们提出了无条件分解和条件分解两种形式，其中条件分解量化了处理在特定协变量水平内的贡献。我们开发了非参数估计量，这些估计量具有$\sqrt{n}$-相合性、渐近正态性、半参数有效性及多重稳健性。我们应用该方法分析了大学教育如何通过因果机制影响代际收入持续性（即高收入与低收入父母子女间的成年收入差异）。实证研究表明，新发现的选择成分在代际收入持续性中发挥着先前未被揭示的作用。