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Controlling for Unmeasured Confounding in Panel Data Using Minimal Bridge Functions: From Two-Way Fixed Effects to Factor Models

Guido Imbens, Nathan Kallus, Xiaojie Mao

arXiv 9 Aug 2021 · Statistics — Methodology · 6 citations (OpenAlex)

arXiv:2108.03849 · PDF · DOI · OpenAlex · Extracted main text

Abstract

We develop a new approach for identifying and estimating average causal effects in panel data under a linear factor model with unmeasured confounders. Compared to other methods tackling factor models such as synthetic controls and matrix completion, our method does not require the number of time periods to grow infinitely. Instead, we draw inspiration from the two-way fixed effect model as a special case of the linear factor model, where a simple difference-in-differences transformation identifies the effect. We show that analogous, albeit more complex, transformations exist in the more general linear factor model, providing a new means to identify the effect in that model. In fact many such transformations exist, called bridge functions, all identifying the same causal effect estimand. This poses a unique challenge for estimation and inference, which we solve by targeting the minimal bridge function using a regularized estimation approach. We prove that our resulting average causal effect estimator is root-N consistent and asymptotically normal, and we provide asymptotically valid confidence intervals. Finally, we provide extensions for the case of a linear factor model with time-varying unmeasured confounders.

Citation extraction

39
references
71
in-text mentions
39
distinct cited
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self-citations
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main-text words

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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
1Yifan Cui, Hongming Pu, Xu Shi, Wang Miao, and Eric Tchetgen Tchetgen (2020) Semiparametric proximal causal inference0.81142100%
2Ben Deaner (2021) Proxy controls and panel data0.81142100%
3Wang Miao, Zhi Geng, and Eric J Tchetgen Tchetgen (2018) Identifying causal effects with proxy variables of an unmeasured confounder0.7373367%
4Alberto Abadie, Alexis Diamond, and Jens Hainmueller (2009) Synthetic control methods for comparative case studies: Estimating the effect of california's tobacco control program0.73732100%
5Eric J Tchetgen Tchetgen, Andrew Ying, Yifan Cui, Xu Shi, and Wang M… (2020) An introduction to proximal causal learning0.73732100%
6Muhammad Jehangir Amjad, Devavrat Shah, and Dennis Shen (2018) Robust synthetic control0.64422100%
7Jeffrey M Wooldridge (2010) Econometric analysis of cross section and panel data0.64422100%
8Susan Athey, Mohsen Bayati, Nikolay Doudchenko, Guido Imbens, and Kh… (2021) Matrix completion methods for causal panel data models self0.58531100%
9Nathan Kallus, Xiaojie Mao, and Masatoshi Uehara (2021) Causal inference under unmeasured confounding with negative controls: A minimax learning approach self0.5113233%
10Ruoxuan Xiong and Markus Pelger (2020) Large dimensional latent factor modeling with missing observations and applications to causal inference0.5113233%

Showing the top 10 of 39 scored citations.

Cited by, within the corpus

arXiv econ.EM papers that cite this one, ranked by how heavily they lean on it.

Citing paperIntensityMentionsSections
1Identification and estimation of treatment effects in a linear factor model with fixed number of time periods1.00064
2Long-term Causal Inference Under Persistent Confounding via Data Combination0.92843
3Treatment Effects in Staggered Adoption Designs with Non-Parallel Trends0.73732
4Identification and Inference for Synthetic Controls with Confounding0.64422
5On the Assumptions of Synthetic Control Methods0.51121
6Causal Models for Longitudinal and Panel Data: A Survey0.51121
7Treatment Effects in Interactive Fixed Effects Models with a Small Number of Time Periods0.40511
8Inference on Strongly Identified Functionals of Weakly Identified Functions0.40511
9Synthetic Blips: Generalizing Synthetic Controls for Dynamic Treatment Effects0.40511
10On the Misspecification of Linear Assumptions in Synthetic Control0.40511