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Nearest Neighbor Matching as Least Squares Density Ratio Estimation and Riesz Regression

Masahiro Kato

arXiv 28 Oct 2025 · Econometrics

arXiv:2510.24433 · PDF · Extracted main text

Abstract

This study proves that Nearest Neighbor (NN) matching can be interpreted as an instance of Riesz regression for automatic debiased machine learning. Lin et al. (2023) shows that NN matching is an instance of density-ratio estimation with their new density-ratio estimator. Chernozhukov et al. (2024) develops Riesz regression for automatic debiased machine learning, which directly estimates the Riesz representer (or equivalently, the bias-correction term) by minimizing the mean squared error. In this study, we first prove that the density-ratio estimation method proposed in Lin et al. (2023) is essentially equivalent to Least-Squares Importance Fitting (LSIF) proposed in Kanamori et al. (2009) for direct density-ratio estimation. Furthermore, we derive Riesz regression using the LSIF framework. Based on these results, we derive NN matching from Riesz regression. This study is based on our work Kato (2025a) and Kato (2025b).

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23
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in-text mentions
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distinct cited
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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
1Zhexiao Lin, Peng Ding, and Fang Han (2023) Estimation based on nearest neighbor matching: from density ratio to average treatment effect1.000235100%
2Victor Chernozhukov, Whitney K. Newey, Victor Quintas-Martinez, and… (2024) Automatic debiased machine learning via riesz regression, 20241.00053100%
3Takafumi Kanamori, Shohei Hido, and Masashi Sugiyama (2009) A least-squares approach to direct importance estimation0.92843100%
4Masahiro Kato (2025) Direct bias-correction term estimation for propensity scores and average treatment effect estimation, 2025a self0.84333100%
5Masahiro Kato (2025) Direct debiased machine learning via bregman divergence minimization, 2025b self0.84333100%
6Alberto Abadie and Guido W. Imbens (2006) Large sample properties of matching estimators for average treatment effects0.64422100%
7Takafumi Kanamori, Taiji Suzuki, and Masashi Sugiyama (2012) Statistical analysis of kernel-based least-squares density-ratio estimation0.58531100%
8Alberto Abadie and Guido W. Imbens (2011) Bias-corrected matching estimators for average treatment effects0.40511100%
9David Bruns-Smith, Oliver Dukes, Avi Feller, and Elizabeth L Ogburn (2025) Augmented balancing weights as linear regression0.40511100%
10Victor Chernozhukov, Whitney K. Newey, and Rahul Singh (2022) Automatic debiased machine learning of causal and structural effects0.40511100%

Showing the top 10 of 23 scored citations.