Differences in Differences (using Stata)

Differences-in-Differences

(v. 3.3)

Oscar Torres-Reyna

otorres@princeton.edu

August 2015



Intro

Differences-in-Differences regression (DID) is used to

asses the causal effect of an event by comparing the

set of units where the event happened (treatment

group) in relation to units where the event did not

happen (control group).

The logic behind DID is that if the event never

happens, the differences between treatment and

control groups should stay the same overtime, see

graph next slide.*

*See:

OTR

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Source:

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? = ?0 + ?1 ???? + ?2 ??????? + ?3 ???? ? ??????? + ?

OTR

Source:

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Intro

This document shows how to perform

difference-in-differences regression in the

following two situations:

? Event happened at the same time for all

treated groups.

? Event is staggered across groups.

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