2x2 Diff-in-Diff

Overview

This module introduces the difference-in-differences identification strategy. We review the basic setup and assumptions necessary for the diff-in-diff estimator to provide a valid estimate of the causal effect. We also survey some of the seminal early applications of diff-in-diff estimation to social policy.

Readings

Impact Evaluation in Practice, first edition: Chapter 6

Optional Readings

Ignaz Semmelweis: the “Savior of Mothers”

Lecture Slides

A handout version of the lecture slides is available here.

Video Lectures from 2021

Lecture 4.1 Intro to Difference-in-Differences Estimation (6:56)

Lecture 4.2 Diff-in-Diff Pioneers (21:19)

Lecture 4.3 Identifying Assumptions for Diff-in-Diff Estimation (13:10)

Lecture 4.4 Diff-in-Diff Examples (20:42)

Empirical Exercise

The in-class activity as a do file or pdf

The empirical exercise as a do file or pdf

A web version of the empirical exercise is available here.