arXivDaily arXiv每日学术速递 周一至周五更新
arXiv周末暂无论文更新,休息一下吧,周末愉快~~
arXiv 2101.09398econ.EMstat.ME
收藏

合成控制方法的基于设计视角研究

A Design-Based Perspective on Synthetic Control Methods

Lea Bottmer, Guido Imbens, Jann Spiess, Merrill Warnick

AI总结:

本文从基于设计的视角研究合成控制方法,指出标准估计量在随机分配下有偏,提出无偏的MUSC估计量及其方差的无偏估计,证实其均方根误差更低,且该提升在处理时期随机选择时有弱保证,可补充模型类方法。

摘要:

自Abadie和Gardeazabal(2003)提出合成控制(Synthetic Control, SC)方法以来,该方法迅速成为面板数据场景下观测研究中估计因果效应的主流方法之一。正式讨论通常以潜在结果由因子模型生成的假设为SC方法提供理论依据。本文从基于设计的视角研究SC方法,假设存在一个处理单元和处理时期的选择模型。我们证明标准SC估计量在随机分配下通常是有偏的。我们提出了一种修正无偏合成控制(Modified Unbiased Synthetic Control, MUSC)估计量,该估计量在随机分配下可保证无偏性,并推导了其基于随机化的精确有限样本方差。我们还提出了该方差的一个无偏估计量。我们在真实数据场景中证实,在随机分配下,SC类估计量的均方根误差可显著低于其他常用估计量。我们证明,若处理时期与其他时期相似(例如处理时期是随机选择的),则这种性能提升是弱保证的。尽管我们的结果仅直接适用于处理随机分配的场景,但我们认为即便对于观测研究,这些结果也能对基于模型的方法形成补充。

英文摘要:

Since their introduction in Abadie and Gardeazabal (2003), Synthetic Control (SC) methods have quickly become one of the leading methods for estimating causal effects in observational studies in settings with panel data. Formal discussions often motivate SC methods by the assumption that the potential outcomes were generated by a factor model. Here we study SC methods from a design-based perspective, assuming a model for the selection of the treated unit(s) and period(s). We show that the standard SC estimator is generally biased under random assignment. We propose a Modified Unbiased Synthetic Control (MUSC) estimator that guarantees unbiasedness under random assignment and derive its exact, randomization-based, finite-sample variance. We also propose an unbiased estimator for this variance. We document in settings with real data that under random assignment, SC-type estimators can have root mean-squared errors that are substantially lower than that of other common estimators. We show that such an improvement is weakly guaranteed if the treated period is similar to the other periods, for example, if the treated period was randomly selected. While our results only directly apply in settings where treatment is assigned randomly, we believe that they can complement model-based approaches even for observational studies.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑