2025/12/24 by Fabrizia Mealli, Javier Viviens, Mealli, Fabrizia +1
Economics, Econometrics and Finance · Mathematics · #Advanced Causal Inference Techniques #Labor market dynamics and wage inequality #Politics, Economics, and Education Policy #econ.EM #stat.ME
paper · pdf · doi:10.48550/arxiv.2512.21176
openalex publication_date 2025/12/24 · openalex created_date 2025/12/26 · openalex updated_date 2026/07/28
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).