论文标题
平行趋势和动态选择
Parallel Trends and Dynamic Choices
论文作者
论文摘要
差异差异是估计治疗效果的常见方法，平行趋势条件是其主要识别假设：平均未处理结果的趋势与观察到的治疗状态无关。在观察环境中，治疗通常是由理性参与者（例如决策者，公司或个人代理人）做出或影响的动态选择。本文将平行趋势与动态选择的经济模型联系起来。当动态选择动机导致违反平行趋势时，我们阐明了平行趋势对代理行为和研究的含义。最后，我们考虑在适应动态选择特征的替代假设下的识别。
Difference-in-differences is a common method for estimating treatment effects, and the parallel trends condition is its main identifying assumption: the trend in mean untreated outcomes is independent of the observed treatment status. In observational settings, treatment is often a dynamic choice made or influenced by rational actors, such as policy-makers, firms, or individual agents. This paper relates parallel trends to economic models of dynamic choice. We clarify the implications of parallel trends on agent behavior and study when dynamic selection motives lead to violations of parallel trends. Finally, we consider identification under alternative assumptions that accommodate features of dynamic choice.
