Policy Evaluation with Nonlinear Trended Outcomes: Covid-19 Vaccination Rates in the United States

IF 3.1 3区经济学 Q2 ECONOMICS

Journal of Applied Econometrics Pub Date : 2025-06-15 DOI:10.1002/jae.3137

Lynn Bergeland Morgan, Peter C. B. Phillips, Donggyu Sul

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Abstract

This paper discusses pitfalls in two way fixed effects (TWFE) regressions when the outcome variables contain nonlinear and possibly stochastic trend components. If a policy change shifts trend paths of outcome variables, TWFE estimation can distort results and invalidate inference, especially in a context of evolving policy decisions. A robust solution is proposed by allowing for dynamic club membership empirically using a relative convergence test procedure. The determinants of respective club memberships are assessed by panel ordered logit regressions. The approach allows for policy evolution and shifts in outcomes according to a convergence cluster framework with transitions over time and the possibility of eventual convergence to a single cluster as policy impacts mature. The long run impact of a policy can thus be examined via its impact on convergence club membership. An application to new weekly US Covid-19 vaccination policy data reveals that federal level vaccine mandates produced a merger of state vaccination rates into a single convergence cluster by mid-September 2021.

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具有非线性趋势结果的政策评估：美国Covid-19疫苗接种率

本文讨论了当结果变量包含非线性和可能随机的趋势成分时，双向固定效应（TWFE）回归的缺陷。如果政策变化改变了结果变量的趋势路径，TWFE估计可能会扭曲结果并使推断无效，特别是在不断发展的政策决策的背景下。通过使用相对收敛测试程序，提出了一个允许动态俱乐部成员的鲁棒解决方案。各俱乐部成员的决定因素是评估面板有序logit回归。该方法允许政策的演变和结果的转变，根据一个收敛集群框架，随着时间的推移而转变，并有可能随着政策影响的成熟最终收敛到一个单一的集群。因此，一项政策的长期影响可以通过其对趋同俱乐部成员的影响来检验。对新的每周美国Covid-19疫苗接种政策数据的申请显示，到2021年9月中旬，联邦一级的疫苗授权导致各州疫苗接种率合并为一个单一的融合簇。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Journal of Applied Econometrics Multiple-

CiteScore

3.70

自引率

4.80%

发文量

期刊介绍： The Journal of Applied Econometrics is an international journal published bi-monthly, plus 1 additional issue (total 7 issues). It aims to publish articles of high quality dealing with the application of existing as well as new econometric techniques to a wide variety of problems in economics and related subjects, covering topics in measurement, estimation, testing, forecasting, and policy analysis. The emphasis is on the careful and rigorous application of econometric techniques and the appropriate interpretation of the results. The economic content of the articles is stressed. A special feature of the Journal is its emphasis on the replicability of results by other researchers. To achieve this aim, authors are expected to make available a complete set of the data used as well as any specialised computer programs employed through a readily accessible medium, preferably in a machine-readable form. The use of microcomputers in applied research and transferability of data is emphasised. The Journal also features occasional sections of short papers re-evaluating previously published papers. The intention of the Journal of Applied Econometrics is to provide an outlet for innovative, quantitative research in economics which cuts across areas of specialisation, involves transferable techniques, and is easily replicable by other researchers. Contributions that introduce statistical methods that are applicable to a variety of economic problems are actively encouraged. The Journal also aims to publish review and survey articles that make recent developments in the field of theoretical and applied econometrics more readily accessible to applied economists in general.