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Beyond Parallel Trends: An Identification-Strategy-Robust Approach to Causal Inference with Panel Data

Brantly Callaway, Derek Dyal, Pedro H. C. Sant'Anna, Emmanuel S. Tsyawo

arXiv 26 Nov 2025 · Econometrics

arXiv:2511.21977 · PDF · DOI · OpenAlex · Extracted main text

Abstract

In this paper, we propose a new approach to causal inference with panel data. Instead of using panel data to adjust for differences in the distribution of unobserved heterogeneity between the treated and comparison groups, we instead use panel data to search for "close comparison groups" -- groups that are similar to the treated group in terms of pre-treatment outcomes. Then, we compare the outcomes of the treated group to the outcomes of these close comparison groups in post-treatment periods. We show that this approach is often identification-strategy-robust in the sense that our approach recovers the ATT under many different non-nested panel data identification strategies, including difference-in-differences, change-in-changes, or lagged outcome unconfoundedness, among several others. We provide related, though non-nested, results under "time homogeneity", where outcomes do not systematically change over time for any comparison group. Our strategy asks more out of the research design -- namely that there exist close comparison groups or time homogeneity (neither of which is required for most existing panel data approaches to causal inference) -- but, when available, leads to more credible inferences.

Citation extraction

34
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Most heavily cited references

The works this paper leans on most, across its whole bibliography — not restricted to papers in our corpus. Ranked by composite intensity, which combines how often a work is mentioned, how many sections mention it, and how much of that falls in the main text rather than the appendix.

ReferenceIntensityMentionsSectionsMain text
1Abadie, Alberto, Diamond, Alexis, Hainmueller, Jens (2010) Synthetic control methods for comparative case studies: Estimating the effect of California’s tobacco control program0.64422100%
2Callaway, Brantly, Sant'Anna, Pedro HC (2021) Difference-in-differences with multiple time periods self0.64422100%
3Callaway, Brantly, Tsyawo, Emmanuel Selorm (2023) Treatment effects in staggered adoption designs with non-parallel trends self0.64422100%
4Athey, Susan, Imbens, Guido (2006) Identification and inference in nonlinear difference-in-differences models0.58531100%
5Arkhangelsky, Dmitry, Athey, Susan, Hirshberg, David A, Imbens, Guid… (2021) Synthetic difference-in-differences0.40511100%
6Arkhangelsky, Dmitry, Imbens, Guido W (2022) Doubly robust identification for causal panel data models0.40511100%
7Arkhangelsky, Dmitry, Imbens, Guido W, Lei, Lihua, Luo, Xiaoman (2024) Design-robust two-way-fixed-effects regression for panel data0.40511100%
8Athey, Susan, Imbens, Guido, Qu, Zhaonan, Viviano, Davide (2025) Triply Robust Panel Estimators0.40511100%
9Callaway, Brantly, Zimmermann, Klaus F (2023) Difference-in-differences for policy evaluation self0.40511100%
10Callaway, Brantly, Li, Tong (2023) Evaluating policies early in a pandemic: Bounding policy effects with nonrandomly missing data self0.40511100%

Showing the top 10 of 34 scored citations.