论文标题
平行趋势何时对功能形式敏感？
When Is Parallel Trends Sensitive to Functional Form?
论文作者
论文摘要
本文评估了差异差异的有效性何时取决于功能形式。我们提供了一种新颖的特征：当且仅当且仅当更强的``平行趋势'''' - 类型条件都具有未经处理的潜在潜在结果的累积分布函数时，平行趋势假设在结果的所有严格单调转换下存在。仅如果可以将种群分配到有效随机分配治疗的亚组中，并且只有将未经处理的潜在结果分布稳定，那么这种情况就可以对功能形式不敏感的形式不敏感。这些条件具有可检验的含义，我们引入了零趋化测试，即平行趋势对功能形式不敏感。
This paper assesses when the validity of difference-in-differences depends on functional form. We provide a novel characterization: the parallel trends assumption holds under all strictly monotonic transformations of the outcome if and only if a stronger ``parallel trends''-type condition holds for the cumulative distribution function of untreated potential outcomes. This condition for parallel trends to be insensitive to functional form is satisfied if and essentially only if the population can be partitioned into a subgroup for which treatment is effectively randomly assigned and a remaining subgroup for which the distribution of untreated potential outcomes is stable over time. These conditions have testable implications, and we introduce falsification tests for the null that parallel trends is insensitive to functional form.
