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Linear Regression with Common Unobserved Heterogeneity

Kaicheng Chen, Hugo Freeman

arXiv 18 Oct 2026 · Econometrics

arXiv:2610.25589 · PDF · Extracted main text

Abstract

We study inference on common slope parameters in linear panel models with two-way unobserved heterogeneity. In linear regression, bias arises from unobserved heterogeneity that is shared between the residual and the covariates. Our common unobserved heterogeneity (CUH) estimator targets this common variation directly: it searches over functionals of the residualised outcome for variation that also resides in the covariates, and seeks to further project out only bias-inducing variation. This makes the estimator less sensitive to weak outcome factors while avoiding the complete removal of exogenous variation in covariates that is unrelated to the confounding heterogeneity. We develop a weak-factor theory based on a singular-value strength index and establish $\sqrt{NT}$-asymptotic normality of the cross-fitted CUH estimator. Under homoskedastic errors, its asymptotic variance is no larger than that of a common correlated effects factor estimator. Simulations and empirical applications illustrate the resulting bias--variance trade-off and the gains from selectively removing common variation.

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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
1Beyhum, Jad and Mugnier, Martin (2025) Inference after discretizing unobserved heterogeneity1.00084100%
2Bai, Jushan (2009) Panel data models with interactive fixed effects0.9416583%
3Freeman, Hugo and Weidner, Martin (2023) Linear panel regressions with two-way unobserved heterogeneity self0.9285480%
4Moon, Hyungsik Roger and Weidner, Martin (2015) Linear Regression for Panel With Unknown Number of Factors as Interactive Fixed Effects0.84333100%
5Bai, Jushan and Ng, Serena (2023) Approximate factor models with weaker loadings0.81142100%
6Freeman, Hugo and Kristensen, Dennis (2026) Inference on Linear Regressions with Two-Way Unobserved Heterogeneity self0.73710640%
7Freeman, Hugo and Kristensen, Dennis (2026) Nonparametric Identification of Two-Way Unobserved Heterogeneity self0.7375340%
8Onatski, Alexei (2012) Asymptotics of the principal components estimator of large factor models with weakly influential factors0.7373367%
9Armstrong, Timothy B and Weidner, Martin and Zeleneev, Andrei (2026) Robust estimation and inference in panels with interactive fixed effects0.64422100%
10Chiang, Harold D. and Hansen, Bruce E. and Sasaki, Yuya (2024) Standard Errors for Two-Way Clustering with Serially Correlated Time Effects0.5112250%

Showing the top 10 of 52 scored citations.