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Differences-in-differences (DiD) is a causal inference method for observational longitudinal data that assumes parallel expected potential outcome trajectories between treatment groups under the counterfactual scenario where all units…

Methodology · Statistics 2026-05-12 Michael Jetsupphasuk , Didong Li , Michael G. Hudgens

We propose a new method for estimating causal effects in longitudinal/panel data settings that we call generalized difference-in-differences. Our approach unifies two alternative approaches in these settings: ignorability estimators (e.g.,…

Methodology · Statistics 2023-12-12 Denis Agniel , Max Rubinstein , Jessie Coe , Maria DeYoreo

The difference-in-differences (DID) method identifies the average treatment effects on the treated (ATT) under mainly the so-called parallel trends (PT) assumption. The most common and widely used approach to justify the PT assumption is…

Econometrics · Economics 2023-08-23 Kyunghoon Ban , Désiré Kédagni

Popular empirical strategies for policy evaluation in the panel data literature -- including difference-in-differences (DID), synthetic control (SC) methods, and their variants -- rely on key identifying assumptions that can be expressed…

Econometrics · Economics 2025-11-11 Yiqi Liu

This paper analyzes difference-in-differences designs with a continuous treatment. We show that treatment-on-the-treated-type parameters are identified under a parallel trends assumption analogous to the binary treatment case. However,…

Econometrics · Economics 2026-01-05 Brantly Callaway , Andrew Goodman-Bacon , Pedro H. C. Sant'Anna

Suppose it is of interest to characterize effect heterogeneity of an intervention across levels of a baseline covariate using only pre- and post- intervention outcome measurements from those who received the intervention, i.e. with no…

Methodology · Statistics 2023-06-21 Zach Shahn

Violations of the parallel trends assumption pose significant challenges for causal inference in difference-in-differences (DiD) studies, especially in policy evaluations where pre-treatment dynamics and external shocks may bias estimates.…

Methodology · Statistics 2025-08-06 Seong Woo Han , Nandita Mitra , Gary Hettinger , Arman Oganisian

Difference-in-Differences (DID) research designs usually rely on variation of treatment timing such that, after making an appropriate parallel trends assumption, one can identify, estimate, and make inference about causal effects. In…

Econometrics · Economics 2020-09-07 Michelle Marcus , Pedro H. C. Sant'Anna

Difference-in-differences is undoubtedly one of the most widely used methods for evaluating the causal effect of an intervention in observational (i.e., nonrandomized) settings. The approach is typically used when pre- and post-exposure…

Methodology · Statistics 2023-08-21 Eric Tchetgen Tchetgen , Chan Park , David Richardson

Difference-in-differences (DiD) is a popular approach to evaluate treatment effects in settings where both pre- and post-treatment measurements of the outcome are available. Despite its popularity, existing methods face important…

Methodology · Statistics 2026-03-31 Chan Park , Eric Tchetgen Tchetgen

In economic program evaluation, it is common to obtain panel data in which outcomes are indicators that an individual has reached an absorbing state. For example, they may indicate whether an individual has exited a period of unemployment,…

Econometrics · Economics 2026-05-26 Ben Deaner , Hyejin Ku

This paper proposes a novel approach for estimating treatment effects in panel data settings, addressing key limitations of the standard difference-in-differences (DID) approach. The standard approach relies on the parallel trends…

Econometrics · Economics 2026-01-14 Shoya Ishimaru

Difference-in-differences (DID) approaches are widely used for estimating causal effects with observational data before and after an intervention. DID traditionally estimates the average treatment effect among the treated after making a…

Methodology · Statistics 2025-06-24 Julia C. Thome , Andrew J. Spieker , Peter F. Rebeiro , Chun Li , Tong Li , Bryan E. Shepherd

Many policy evaluations involve vectors of category-specific quantities, either categorical outcomes (e.g., employment type, major choice) or compositional measures (e.g., GDP by sector, votes by party, electricity generation by source). In…

Econometrics · Economics 2026-02-19 Onil Boussim

Remarkable progress has been made in difference-in-differences (DID) approaches to causal inference that estimate the average effect of a treatment on the treated (ATT). Of these, the semiparametric DID (SDID) approach incorporates a…

Methodology · Statistics 2026-03-09 Takamichi Baba , Yoshiyuki Ninomiya

A popular method for estimating a causal treatment effect with observational data is the difference-in-differences (DiD) model. In this work, we consider an extension of the classical DiD setting to the hierarchical context in which data…

Methodology · Statistics 2019-10-17 James Normington , Eric F. Lock , Thomas A. Murray , Caroline S. Carlin

Identifying effects of actions (treatments) on outcome variables from observational data and causal assumptions is a fundamental problem in causal inference. This identification is made difficult by the presence of confounders which can be…

Methodology · Statistics 2012-03-19 Ilya Shpitser , Tyler VanderWeele , James M. Robins

Drawing causal inference with observational studies is the central pillar of many disciplines. One sufficient condition for identifying the causal effect is that the treatment-outcome relationship is unconfounded conditional on the observed…

Statistics Theory · Mathematics 2017-01-17 Peng Ding , Tyler VanderWeele , James Robins

The method of difference-in-differences (DID) is widely used to study the causal effect of policy interventions in observational studies. DID employs a before and after comparison of the treated and control units to remove bias due to…

Methodology · Statistics 2022-06-15 Ting Ye , Luke Keele , Raiden Hasegawa , Dylan S. Small

Applied analysts often use the differences-in-differences (DID) method to estimate the causal effect of policy interventions with observational data. The method is widely used, as the required before and after comparison of a treated and…

Applications · Statistics 2019-02-04 Luke J. Keele , Dylan S. Small , Jesse Y. Hsu , Colin B. Fogarty