随着 did 方法的拓展，许多实证研究将其拓展为多期 did，即实验组并非在同一时点遭受政策冲击。 但是，自 2019 年来，不少学者纷纷指出这种多期 did 有可能会产生有偏估计 (athey and. 经济学季刊对双重差分did和工具变量法iv中的表述做出了要求。 一、双差分、事件研究等双向固定效应模型中的平行趋势假设 （1）反事实基础与不可直接检验… 显示全部 关注者 18 被浏览.
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