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At What Level Should One Cluster Standard Errors in Paired and Small-Strata Experiments?

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  • Clément de Chaisemartin
  • Jaime Ramirez-Cuellar

Abstract

In clustered paired experiments, randomization units, say villages, are matched into pairs, and one unit of each pair is randomly assigned to treatment. To estimate the treatment effect, researchers often regress their outcome on the treatment and pair fixed effects, clustering standard errors at the unit-of-randomization level. We show that the variance estimator in this regression may be severely downward biased: under constant treatment effect, its expectation equals 1/2 of the true variance. Instead, researchers should cluster at the pair level. Using simulations, we show that those results extend to clustered stratified experiments with few units per strata.

Suggested Citation

  • Clément de Chaisemartin & Jaime Ramirez-Cuellar, 2020. "At What Level Should One Cluster Standard Errors in Paired and Small-Strata Experiments?," NBER Working Papers 27609, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberwo:27609
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    3. James G. MacKinnon & Morten Ørregaard Nielsen & Matthew D. Webb, 2020. "Testing for the appropriate level of clustering in linear regression models," Working Paper 1428, Economics Department, Queen's University.
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    5. Meinzen-Dick, Laura, 2020. "Decentralization and Elections in Burkina Faso," 2020 Annual Meeting, July 26-28, Kansas City, Missouri 304447, Agricultural and Applied Economics Association.
    6. Alice Guerra & Tatyana Zhuravleva, 2022. "Do women always behave as corruption cleaners?," Public Choice, Springer, vol. 191(1), pages 173-192, April.
    7. Lafortune, Jeanne & Pugatch, Todd & Tessada, José & Ubfal, Diego, 2022. "Can interactive online training make high school students more entrepreneurial? Experimental evidence from Rwanda," GLO Discussion Paper Series 1041, Global Labor Organization (GLO).
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    9. Yuehao Bai & Jizhou Liu & Max Tabord-Meehan, 2022. "Inference for Matched Tuples and Fully Blocked Factorial Designs," Papers 2206.04157, arXiv.org, revised Oct 2022.

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    More about this item

    JEL classification:

    • C01 - Mathematical and Quantitative Methods - - General - - - Econometrics
    • C21 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables - - - Cross-Sectional Models; Spatial Models; Treatment Effect Models

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