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Time-Weighted Difference-in-Differences: Accounting for Common Factors in Short T Panels

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  • Timo Schenk

    (University of Amsterdam)

Abstract

This paper proposes a time-weighted difference-in-differences (TWDID) estimation approach that is robust against interactive fixed effects in short T panels. Time weighting substantially reduces both bias and variance compared to conventional DID estimation through balancing the pre-treatment and post-treatment unobserved common factors. To conduct valid inference on the average treatment effect, I develop a correction term that adjusts conventional standard errors for weight estimation uncertainty. Revisiting a study on the effect of a cap-and-trade program on NOx emissions, TWDID estimation reduces the standard errors of the estimated treatment effect by 10% compared to a conventional DID approach. In a second application I illustrate how to implement TWDID in settings with staggered adoption of the treatment.

Suggested Citation

  • Timo Schenk, 2023. "Time-Weighted Difference-in-Differences: Accounting for Common Factors in Short T Panels," Tinbergen Institute Discussion Papers 23-004/III, Tinbergen Institute.
    • Handle: RePEc:tin:wpaper:20230004
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    References listed on IDEAS

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    Keywords

    synthetic difference-in-differences; dynamic treatment effects; interactive fixed effects; panel data;
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