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What's Logs Got to do With it: On the Perils of log Dependent Variables and Difference-in-Differences

Brendon McConnell

arXiv 31 Jul 2023 · Econometrics · 11 citations (OpenAlex)

arXiv:2308.00167 · PDF · DOI · OpenAlex · Extracted main text

Abstract

The log transformation of the dependent variable is not innocuous when using a difference-in-differences (DD) model. With a dependent variable in logs, the DD term captures an approximation of the proportional difference in growth rates across groups. As I show with both simulations and two empirical examples, if the baseline outcome distributions are sufficiently different across groups, the DD parameter for a log-specification can be different in sign to that of a levels-specification. I provide a condition, based on (i) the aggregate time effect, and (ii) the difference in relative baseline outcome means, for when the sign-switch will occur.

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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
1Emanuele Ciani and Paul Fisher Dif-in-dif estimators of multiplicative treatment effects0.84333100%
2Bruce D. Meyer (1995) Natural and quasi-experiments in economics0.81142100%
3Ariella Kahn-Lang and Kevin Lang (2020) The promise and pitfalls of differences-in-differences: Reflections on 16 and pregnant and other applications0.73732100%
4Jonathan Roth and Pedro H. C. Sant'Anna (2023) When is parallel trends sensitive to functional form?0.73732100%
5Joshua D Angrist and Jörn-Steffen Pischke (2009) Mostly harmless econometrics: An empiricist's companion0.40511100%
6H. Spencer Banzhaf (2021) Difference-in-differences hedonics0.40511100%
7Marc F. Bellemare and Casey J. Wichman (2020) Elasticities and the inverse hyperbolic sine transformation0.40511100%
8Kelly C. Bishop, Nicolai V. Kuminoff, H. Spencer Banzhaf, Kevin J. B… (2020) Best practices for using hedonic property value models to measure willingness to pay for environmental quality0.40511100%
9Amy Finkelstein (2007) The Aggregate Effects of Health Insurance: Evidence from the Introduction of Medicare*0.40511100%
10Andrew Goodman-Bacon (2021) Difference-in-differences with variation in treatment timing0.40511100%

Showing the top 10 of 65 scored citations.