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Contribution Details

Type Journal Article
Scope Discipline-based scholarship
Title Neglected heterogeneity, Simpson’s paradox, and the anatomy of least squares
Organization Unit
Authors
  • Rainer Winkelmann
Item Subtype Original Work
Refereed Yes
Status Published electronically before print/final form (Epub ahead of print)
Language
  • English
Journal Title Journal of Econometric Methods
Publisher De Gruyter
Geographical Reach international
ISSN 2156-6674
Page Range Epub ahead of print
Date 2023
Abstract Text When a sample combines data from two or more groups, multivariate regression yields a matrix-weighted average of the group-specific coefficient vectors. However, it is possible that the weighted average of a specific coefficient falls outside the range of the group-specific coefficients, and it may even have a different sign compared to both group-level coefficients, a manifestation of Simpson’s paradox. The result of the combined regression is then prone to misinterpretation. The purpose of this paper is to raise awareness of this problem and to state conditions under which such non-convex weighting or sign reversal can arise, for a model with two regressors and two groups. Two illustrative examples, an investment equation estimated with panel data, and a cross-sectional earnings equation for men and women, highlight the relevance of these findings for applied work.
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Digital Object Identifier 10.1515/jem-2023-0028
Other Identification Number merlin-id:24387
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Keywords Applied mathematics, economics and econometrics, statistics and probability, average treatment effect, covariance-weighting, heterogeneity spillover, non-convex average