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Interpreting OLS Estimands When Treatment Effects Are Heterogeneous: Smaller Groups Get Larger Weights

Tymon Słoczyński

arXiv 3 Oct 2018 · Econometrics · publishedThe Review of Economics and Statistics (2020) · 73 citations (OpenAlex)

arXiv:1810.01576 · PDF · DOI · OpenAlex · Extracted main text

Abstract

Applied work often studies the effect of a binary variable ("treatment") using linear models with additive effects. I study the interpretation of the OLS estimands in such models when treatment effects are heterogeneous. I show that the treatment coefficient is a convex combination of two parameters, which under certain conditions can be interpreted as the average treatment effects on the treated and untreated. The weights on these parameters are inversely related to the proportion of observations in each group. Reliance on these implicit weights can have serious consequences for applied work, as I illustrate with two well-known applications. I develop simple diagnostic tools that empirical researchers can use to avoid potential biases. Software for implementing these methods is available in R and Stata. In an important special case, my diagnostics only require the knowledge of the proportion of treated units.

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34
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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
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3Angrist, J. D (1998) Estimating the labor market impact of voluntary military service using Social Security data on military applicants0.87421367%
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5LaLonde, R. J (1986) Evaluating the econometric evaluations of training programs with experimental data0.81142100%
6Aronow, P. M. and Samii, C (2016) Does regression produce representative estimates of causal effects?0.7639344%
7Card, D., Kluve, J., and Weber, A (2018) What works? A meta analysis of recent active labor market program evaluations0.73732100%
8Dehejia, R. H. and Wahba, S (1999) Causal effects in nonexperimental studies: Reevaluating the evaluation of training programs0.73732100%
9Deaton, A (1997) The Analysis of Household Surveys: A Microeconometric Approach to Development Policy0.6445240%
10Solon, G., Haider, S. J., and Wooldridge, J. M (2015) What are we weighting for?0.6445240%

Showing the top 10 of 34 scored citations.

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Citing paperIntensityMentionsSections
1Demystifying and avoiding the OLS “weighting problem”: Unmodeled heterogeneity and straightforward solutions1.00053
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