本次课程中,江老师将用一天的时间,介绍敏感性分析的核心理念、概念,常用的分析方法,以及 Stata 实现过程。
Q2. 课程中 DID 部分有何亮点?
DID 的发展非常快。现在看来,很多早期文献中使用 TWFE 等估计方法存在严重缺陷,甚至在某些情况下得到的结果存在严重偏误。本次课程将用两天的时间,帮各位梳理清楚近几年新提出的各类 DID 方法的应用场景、适用条件。
更为重要的是,在应用场景最广泛的交错 DID 中,需要谨慎地进行模型设定和诊断,否则很难证明结果的合理性。在讲解过程中,江老师会结合经典论文的复现和拆解,辅以 Stata 代码的解读,以便各位能将这些模型正确、规范地应用于自己的研究之中。这部分的涉及的文献包括经典的 Qian (2008),Duflo (2001),以及最新的 Sun and Abraham (2020),Wooldridge (2021),Callaway and Sant'Anna (2021); Borusyak et al (2023) 等论文。
Q3. 课程中 IV 部分有何亮点?
IV 很强大,用好不容易!在早期经典文献中,大家似乎只能靠「天赐良机」,比如 Angrist 教授用「出生季度」作为教育水平的工具变量;Acemoglu 教授用「死亡率」作为制度的工具变量。没有绝顶聪明的脑袋,似乎是无法找到「干净的」工具变量的。
Bartik IV,也叫「Shift-Share IV, SSIV」,近几年频频出现在国际贸易、环境经济、劳动经济等多个领域的 Top 期刊上。例如,要研究美国各州的工资增长率与劳动力供给之间的关系,就必须克服后者的内生性问题。Bartik IV 的思路是使用外部冲击构造 IV。这里的冲击源于中国对美国的进口额 (Shift),具有较强的外生性。同时,考虑到每个行业受到的「中国制造」的冲击程度不同,就可以用美国各州各个行业的劳动力份额作为权重 (Share),以衡量暴露程度。二者之积便是所谓的 Bartik IV。推而广之,但凡可以找到一个相对外生的 Shock,加上本土早期的 Share,就可以构造出 IV 了。得益于 Goldsmith-Pinkham et al (2020); Borusyak et al (2022) 的论证工作,这一套方法具有扎实的理论基础。
GIV。另一个最近两年频繁现身于 JPE, AER, RES, RFS 等期刊的工具变量是「颗粒 IV」(Granular IV, GIV)。其基本思想是,经济体系中那些头部行业 (企业) 的大幅波动会对其他行业 (企业) 产生异质性冲击,我们可以通过一些技术上的处理,将每个行业 (企业) 的干扰项分解成共同冲击和个体冲击,进而以此为基础构造工具变量。GIV 在基本思想上与 Bartik IV 有几分相似,但不需要从我们所研究的经济体之外去找新的 Shock,构造过程也有更清晰的计量基础。
与之相似的 IV 构造方法还包括法官效应 IV (JEIV),基于模拟的 IV (SIV) 等。
当然,江老师的课程中还会涉及如工具变量问题,以及「排他性约束」的检验和识别问题。这都是近期应用 IV 的文献必须应对的问题。
2. 嘉宾简介
江艇,香港科技大学商学院经济学博士,中国人民大学经济学院副教授,人大国家发展与战略研究院研究员,人大微观数据与实证方法研究中心副主任,美国哥伦比亚大学商学院访问学者。主要研究领域为经济增长与发展、城市经济学、新政治经济学,在 Economics Letters、Review of Development Economics、《经济研究》、《管理世界》、《世界经济》等国内外著名学术刊物上发表多篇论文,曾应邀在多所高校讲授「应用微观计量经济学」短期前沿课程,被誉为「醍醐大师」。
3. 课程详情
专题一:敏感性分析(1 天)
控制回归是因果识别中最基础的方法,但其中的关键假设——“无混淆性”往往难以验证。在这种情况下,我们需要考虑在「无混淆性」假设无法完全得到满足的各种场景下,因果效应估计结果会发生怎样变化,这些变化是否会对研究结论产生实质性影响?这就是所谓的「敏感性分析」,它已经成为 Top 期刊论文中除了稳健性检验和异质性分析 之外的另一个必要内容。本专题将系统介绍几种主要的敏感性分析方法和工具,包括它们的统计含义、联系与区别,以及在 Stata 中的实现方法和扩展应用,包括如下几个主题:
基于系数估计值的方法:
Bellows and Miguel (2009); Nunn and Wantchekon (2012)
基于相关系数的方法:
Altonji et al (2005);
Aidt and Franck (2015)
双参数方法:Oster (2019)
基于拟合优度的方法:Cinelli and Hazlett (2020)
专题二:双重差分的三大难点及应对(2 天)
双重差分方法因果识别中应用最为广泛的方法,它易于上手,却难于精通。本专题将重点讨论该方法应用中的三大难点: 其一, DID 的各种变体分别适用于哪些应用场景? 其二, 如何理解和选择新近提出的各类「交错 DID」方法? 其三, 如何论证「平行趋势假设」?
Aidt, Toke S, and Raphael Franck. 2015. "Democratization Under the Threat of Revolution: Evidence From the Great Reform Act of 1832." Econometrica. -Link-, -PDF-
Altonji, Joseph G, Todd E Elder, and Christopher R Taber. 2005. "Selection on Observed and Unobserved Variables: Assessing the Effectiveness of Catholic Schools." Journal of Political Economy. -Link-, -PDF-, PDF2
Angrist, Joshua, and Michal Kolesar. 2022. "One Instrument to Rule Them All: The Bias and Coverage of Just-ID IV." Journal of Econometrics (forthcoming). -Link-, -PDF-
Arkhangelsky, D., S. Athey, D. A. Hirshberg, G. W. Imbens,S. Wager, 2021, Synthetic difference-in-differences, American Economic Review, 111 (12): 4088-4118. -Link-, -PDF-, Replication
Bellows, John, and Edward Miguel. 2009. "War and local collective action in Sierra Leone." Journal of Public Economics. -Link-, -PDF-
Borusyak, Kirill, and Peter Hull. 2022. "Non-Random Exposure to Exogenous Shocks." -Link-, -PDF-, PDF2
Borusyak, K., P. Hull, X. Jaravel, 2022, Quasi-experimental shift-share research designs, Review of Economic Studies, 89 (1): 181-213. -Link-, -PDF-
Borusyak, Kirill, Xavier Jaravel, and Jann Spiess. 2023. "Revisiting Event Study Designs: Robust and Efficient Estimation." -Link-, -PDF-
Callaway, B., P. H. C. Sant'Anna, 2021, Difference-in-differences with multiple time periods, Journal of Econometrics, 225 (2): 200-230. -Link-, -PDF-, PDF2
Card, D., A. B. Krueger, 1994, Minimum wages and employment: A case study of the fast-food industry in new jersey and pennsylvania, The American Economic Review, 84 (4): 772-793. -Link-, -PDF-, PDF2
Cengiz, D., A. Dube, A. Lindner, B. Zipperer, 2019, The effect of minimum wages on low-wage jobs, Quarterly Journal of Economics, 134 (3): 1405-1454. -Link-, -PDF-, Replication
Cinelli, Carlos, and Chad Hazlett. 2020. "Making sense of sensitivity: extending omitted variable bias." Jounrnal of the Royal Statistical Society Series B: Statistical Methodology. -Link-, -PDF-
Currie, Janet, and Jonathan Gruber. 1996. "Health Insurance Eligibility, Utilization of Medical Care, and Child Health." Quarterly Journal of Economics. -Link-, -PDF-
Dobbie, Will, Paul Goldsmith-Pinkham, Crystal S Yang. 2017. "Consumer Bankruptcy and Financial Health." Review of Economics and Statistics. -Link-, -PDF-
Duflo, Esther. 2001. "Schooling and Labor Market Consequences of School Construction in Indonesia: Evidence From an Unusual Policy Experiment." American Economic Review. -Link-, -PDF-
Fetter, Daniel K, and Lee M Lockwood. 2018. "Government Old-Age Support and Labor Supply: Evidence from the Old Age Assistance Program." American Economic Review. -Link-, -PDF-, PDF2, Replication
Freyaldenhoven, Simon, Chris B Hansen, Jorge Perez Perez, and Jesse M Shapiro. 2021. "Visualization, Identification, and Estimation in the Linear Panel Event Study Design." -Link-, -PDF-
Freyaldenhoven, Simon, Christian B Hansen, and Jesse M Shapiro. 2019. "Pre-Event Trends in the Panel Event-Study Design." American Economic Review. -Link-, -PDF-, Replication
Fowlie, Meredith, Stephen P Holland, and Erin T Mansur. 2012. "What Do Emissions Markets Deliver and to Whom? Evidence From Southern California's NOx Trading Program." American Economic Review. -Link-, -PDF-, Appendix, Replication
Gabaix, Xavier and Ralph S J Koijen. 2023. "Granular Instrumental Variables." -Link-, -PDF-
Gabaix, Xavier and Ralph S J Koijen. 2022. "In Search of the Origins of Financial Fluctuations: The Inelastic Markets Hypothesis." -Link-, -PDF-
Goldsmith-Pinkham, P., I. Sorkin, H. Swift, 2020, Bartik instruments: What, when. Why, and how, American Economic Review, 110 (8): 2586-2624. -Link-, -PDF-, PDF2, Replication, -cited-
Goodman-Bacon, A., 2021, Difference-in-differences with variation in treatment timing, Journal of Econometrics, 225 (2): 254-277. -Link-, -PDF-
van Kippersluis, Hans, and Cornelius A Rietveld. 2018. "Beyond plausibly exogenous." Econometrics Journal. -Link-, -PDF-
Lee, David S, Justin McCrary, Marcelo J Moreira, and Jack Porter. 2022. "Valid t-Ratio Inference for IV." American Economic Review. -Link-, -PDF-, Appendix, Replication
Muralidharan, Karthik, and Nishith Prakash. 2017. "Cycling to School: Increasing Secondary School Enrollment for Girls in India." American Economic Journal: Applied Economics. -Link-, -PDF-, Appendix, Replication
Nunn, Nathan, and Nancy Qian. 2014. "US Food Aid and Civil Conflict." American Economic Review. -Link-, -PDF-, Appendix, Replication
Nunn, Nathan, and Nancy Qian. 2011. "The Potato's Contribution to Population and Urbanization: Evidence From a Historical Experiment." Quarterly Journal of Economics. -Link-, -PDF-
Nunn, Nathan, and Leonard Wantchekon. 2011. "The Slave Trade and the Origins of Mistrust in Africa." American Economic Review. -Link-, -PDF-, Appendix, Replication
Oster, Emily. 2019. "Unobservable Selection and Coefficient Stability: Theory and Evidence." Journal of Business & Economic Statistics. -Link-, -PDF-, Appendix
Qian, Nancy. 2008. "Missing Women and the Price of Tea in China: The Effect of Sex-Specific Earnings on Sex Imbalance." Quarterly Journal of Economics. -Link-, -PDF-
Rambachan Ashesh, and Jonathan Roth. 2023. "A More Credible Approach to Parallel Trends." Review of Economic Studies. -Link-, -PDF-, Replication
Stevenson, Megan T. 2018. "Distortion of Justice: How the Inability to Pay Bail Affects Case Outcomes." Journal of Law, Economics, and Organization. -Link-, -PDF-, Appendix
Sun, L., S. Abraham, 2021, Estimating dynamic treatment effects in event studies with heterogeneous treatment effects, Journal of Econometrics, 225 (2): 175-199. -Link-, -PDF-, PDF2
Wooldridge, Jeffrey M, 2021. "Two-Way Fixed Effects, the Two-Way Mundlak Regression, and Difference-in-Differences Estimators." -PDF-