Difference-in-Differences in the Presence of Unknown Interference

Fuente: arXiv
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Auteurs principaux: Mealli, Fabrizia, Viviens, Javier
Format: Preprint
Publié: 2025
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author Mealli, Fabrizia
Viviens, Javier
author_facet Mealli, Fabrizia
Viviens, Javier
contents The stable unit treatment value (SUTVA) is a crucial assumption in the Difference-in-Differences (DiD) research design. It rules out hidden versions of treatment and any sort of interference and spillover effects across units. Even if this is a strong assumption, it has not received much attention from DiD practitioners and, in many cases, it is not even explicitly stated as an assumption, especially the no-interference assumption. In this technical note, we investigate what the DiD estimand identifies in the presence of unknown interference. We show that the DiD estimand identifies a contrast of causal effects, but it is not informative on any of these causal effects separately, without invoking further assumptions. Then, we explore different sets of assumptions under which the DiD estimand becomes informative about specific causal effects. We illustrate these results by revisiting the seminal paper on minimum wages and employment by Card and Krueger (1994).
format Preprint
id arxiv_https___arxiv_org_abs_2512_21176
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Difference-in-Differences in the Presence of Unknown Interference
Mealli, Fabrizia
Viviens, Javier
Econometrics
Methodology
The stable unit treatment value (SUTVA) is a crucial assumption in the Difference-in-Differences (DiD) research design. It rules out hidden versions of treatment and any sort of interference and spillover effects across units. Even if this is a strong assumption, it has not received much attention from DiD practitioners and, in many cases, it is not even explicitly stated as an assumption, especially the no-interference assumption. In this technical note, we investigate what the DiD estimand identifies in the presence of unknown interference. We show that the DiD estimand identifies a contrast of causal effects, but it is not informative on any of these causal effects separately, without invoking further assumptions. Then, we explore different sets of assumptions under which the DiD estimand becomes informative about specific causal effects. We illustrate these results by revisiting the seminal paper on minimum wages and employment by Card and Krueger (1994).
title Difference-in-Differences in the Presence of Unknown Interference
topic Econometrics
Methodology
url https://arxiv.org/abs/2512.21176