IDEAS home Printed from https://ideas.repec.org/a/wly/japmet/v40y2025i6p697-714.html
   My bibliography  Save this article

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

Author

Listed:
  • Lynn Bergeland Morgan
  • Peter C. B. Phillips
  • Donggyu Sul

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.

Suggested Citation

  • Lynn Bergeland Morgan & Peter C. B. Phillips & Donggyu Sul, 2025. "Policy Evaluation with Nonlinear Trended Outcomes: Covid‐19 Vaccination Rates in the United States," Journal of Applied Econometrics, John Wiley & Sons, Ltd., vol. 40(6), pages 697-714, September.
    • Handle: RePEc:wly:japmet:v:40:y:2025:i:6:p:697-714
    DOI: 10.1002/jae.3137
    as

    Download full text from publisher

    File URL: https://doi.org/10.1002/jae.3137
    Download Restriction: no
    File URL: https://libkey.io/10.1002/jae.3137?utm_source=ideas
    LibKey link: if access is restricted and if your library uses this service, LibKey will redirect you to where you can use your library subscription to access this item
    ---><---

    More about this item

    Statistics

    Access and download statistics

    Corrections

    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:wly:japmet:v:40:y:2025:i:6:p:697-714. See general information about how to correct material in RePEc.

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    We have no bibliographic references for this item. You can help adding them by using this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: Wiley Content Delivery (email available below). General contact details of provider: http://www.interscience.wiley.com/jpages/0883-7252/ .

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service. RePEc uses bibliographic data supplied by the respective publishers.