Questions tagged [difference-in-difference]

Often abbreviated DID or DD, this is a technique for inferring causality from observational data. It involves comparing measurements before and after a treatment occurs (hence, the growth rate) in both a group that received the treatment, and an otherwise comparable group that did not.

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Leads and Lags in a Staggered Difference-in-Differences Model Stata

I'm trying to use: 1) lags to check whether the effect increases or decreases over time, and 2) leads to check for parallel trends. I'm thinking that regressing each dummy (0 years after treatment, 1 ...
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Adding Controls to Staggered Difference in Difference Regressions on Stata

I am running a staggered diff-in-diff model, looking at legalization's effect on various variables. For context, only a percentage of all states have legalized, and the year they legalized differs ...
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Long-term event study vs Difference in Differences (DID) analysis

I am trying to understand the differences between event studies and DID analysis. In particular, if I want to estimate the specific effect of an event like certification adoption, CEO appointment, or ...
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Simplified DID: How to run significance test

If we know that Variable C = Variable A - Variable B, and Variable A is the difference in two groups (binary data) during time period X. It is statistically significant. Variable B is the difference ...
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DiD for multiple times and states

I am currently looking at this paper: https://www.nature.com/articles/s41591-021-01487-3 The equation for (1) includes a variable for a baseline value. This is using a regular OLS. I am interested in ...
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Difference in difference with multiple treatments

I have a setting in which there are three disjoint groups as follows; (1) a group which does not experience any change, i.e., controls, (2) a group who receives treatment 1, and (3) and a group who ...
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Difference-in-differences if the control group is treated later

Would a difference-in-differences analysis still tell me something important if the control group was treated later in time? Or, would I be better off only restricting my analysis to the time frame up ...
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Difference In Differences with Daily Numbers

I ran a DID regression and found my estimate on the DID coefficient to be .022. The units of time I am using are days, and at a certain day around halfway through my data, the treatment group was ...
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Interpretation of Relative Difference in Differences Results with Relative Units

I am writing a paper using a difference-in-differences analysis. My control and treatment groups are groups of 7 or 6 states that either do not or do undergo a certain policy. I ran my difference-in-...
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Difference-in-differences length for pre and post period

For difference-in-differences, do we need to select same duration/length for Pre period compared to Post period? For example, if post period is 5 months, do we need to select pre period to be of 5 ...
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Nested Individuals within a group - meaning?

I am reading "DID Intro" by Stata Corp LLC. It is recently updated, early April 2022. On page 7, it explains how Stata runs a panel-data difference-in-differences regression. My question is ...
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Placebo test for triple DiD regression

I am currently trying to run a regression working out the change in the mental well-being of ethnic individuals in a set of countries after a migration policy was imposed. I have two waves of data, ...
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How is a difference-in-differences model represented in a causal diagram (or directed acyclic graph)?

Unlike a standard causal model with A = Treatment, X = Confounder, and Y = Outcome: a difference-in-differences (DiD) model is concerned with estimating the Average Treatment Effect on the Treated (...
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Hypothesis test for difference-of-differences of proportions?

I know how to perform a test of the difference between two proportions. This is one level more complex than that. I have an experiment in which participants (male or female) are randomly assigned to ...
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Difference and difference with multiple time period

I would like to know if someone has a solution for running a difference in difference model in R with variation in treatment timing. I mean, normally a treatment dummy and a post treatment dummy ...
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What is the difference between constrained and unconstrained models

I have a question what is the difference between constrained and unconstrained model or freely estimated model. I am trying to test for chi square difference between them to determine discriminant ...
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Struggle with use of event study approach with non-firm data

I am attempting to use event study combined with difference in difference analyses to assess the parallel trend assumption in an individual level analyses of the impact of COVID on monthly income. The ...
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Interpreting coefficient in a Diff-in-Diff (fixed effects model)

I am running a DiD model with fixed effects to find the causal effect of traffic cameras on my outcome variable: share of car accidents of total accidents per neighborhood. The treatment, road cameras,...
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difference in difference: multiple treatment on the same unit

I am trying to evaluate the effect of a policy, say the minimum wage during multiple periods. I have three types of states: Some states may experience multiple treatments at various stages. (for ...
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Estimating time invariate variablies in difference-in-differences with fixed effects

I am using the following fixed effects model that has intercept and slope coefficient that vary across individuals. $Y_{it}$ - dependent vector variable for monthly income for individual i at time t. ...
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What pre-/post-treatment cohorts should I include in a generalised diff-in-diff with treatment on cohort level?

I analyse an educational policy that shortened mandatory schooling. The rollout of the reform happened over 3 subsequent years in different states ($c=0$ is the last graduation cohort pre-reform, $c=3$...
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Robustness checks for DiD

I am currently looking at a DiD model to evaluate the impact of a policy on ethnic and non ethnic people in the EU. I have done the regression and got the results. I have only two time periods but 10 ...
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Methods for evaluating a geo-experimental research design (DiD, CausalImpact or a third option?)

I'm doing my undergraduate thesis on an experimental design of the incrementality of clicks using Google Ads vs not using Google Ads. I've created a geo-experimental design, where I've made a split of ...
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Is my differences-in-differences model viable?

I'm currently an undergrad writing my senior thesis, so forgive my ignorance. Basically, I'm trying to calculate the effects of Elon Musk's tweets on dogecoin prices, especially in comparison to ...
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Matching on pre-treatment outcome $z$-score in diff-in-diff analysis to avoid regression toward the mean bias in $ATT$ estimates?

There have been many articles (e.g., Chabé-Ferret (2017), Daw & Hatfield (2018), Zeldow & Hatfield (2021)) discussing the perils of matching on pre-treatment outcomes (such as patient's ...
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Triple Difference-in-differences

I am currently trying to run a regression working out the change in the mental well-being of ethnic individuals in a set of countries after a migration policy was imposed. I have two waves of data, ...
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Difference-in-difference covariates affecting outcome but failing parallel trends

I am performing a difference-in-difference analysis and, as advised by this post, ran my regression with each of my covariates as the outcome. I did this for each covariate individually using the ...
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Making difference-in-differences(DiD) table like Card&Kruger(1994)

My team is using difference-in-differences(DiD) method for our empirical project. Before we show the regression DiD results, we wish to present 3X3 table - like in Card&Krueger(1994) - which shows ...
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Minimum sample size of an observation in an unbalanced panel

I created an unbalanced panel from my raw data with several million cases. In this panel, each observation represents one city in one month. For some cities and months, only 5 cases are available as a ...
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Impact of COVID-19 on different groups using a Difference-In-Difference setting

This post provides a clear explanation of a difference-in-difference setting where two similar groups (one with a certain attribute and the other without) are differently affected by the COVID-19 ...
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Matching fixed control group to multiple time-varying treatment events so that each control is only used once/uniquely assigned

you have helped me tremendously over the past years and so far, I could find an answer to any the question I had! Thanks to anyone active in this community, I don't know what I would have done without ...
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Addressing parallel trends violation Diff in Diff

I am analyzing the impact of a tax policy, and when I run the conventional DiD model, I see that there is a negative and statistically negative effect of 1.9. But when I visually checked pre-...
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What statistical test to use

I want to carry out a study but I don’t know which statistical method to use for analysing the results. I have two buildings (say, houses A and B) and I keep daily records of some quantitative ...
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What is the right econometric model to use

I want to evaluate how the cultivation of a particular crop has impacted several socioeconomic variables at the municipality level. I have a map that identifies the municipalities where this crop can ...
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Is diff-in-diff applicable in this case?

Suppose I want to learn the effect of land confiscation from church on education investment. I have data on all land expropriated by the government from churches, so I can see which municipalities ...
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Distinction between Treatment and Control Group

I am struggling to understand how to interpret the treatment and control group in the following case of DID regression. We need to estimate the causal effect of brick kilns on downwind PM2.5 monitor ...
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Impact evaluation: non-traditional regression equation framework

I have a panel data of households. Meaning I have records of many households over multiple weeks. For the first six weeks no household received any treatment. For next six weeks all households ...
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Continuous variable Treatment Group in DID Regression [duplicate]

I am struggling to understand how to interpret the treatment and control group in the following case of DID regression. We need to estimate the causal effect of brick kilns on downwind PM2.5 monitor ...
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1 vote
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Difference-in-difference regression with pooled cross sectional data - fixed effects

I'm trying to estimate a difference-in-difference model with pooled cross-sectional data. The dataset consists of rental prices in one city for the years of 2011-2021 and includes a wide range of ...
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Purpose of differences in differences with multiple time dummies

I understand that the standard difference in differences with 2 groups, 2 time periods appears as follows \begin{align*} y = \beta_0 + \beta_1Tr + \beta_2Post + \beta_3 Tr \times Post + u \end{align*} ...
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Propensity Score Matching with Covariates pre-treatment

I am applying a propensity score matching on R using the package Matchit. I read that to match the observations, you should take the covariates and balance them. However, only pre-treatment ...
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Is parallel trends assumption necessary in difference-in-differences analysis?

Reading the literature on the subject, I haven't encountered clear reasoning why the parallel trends assumption must hold. In fact, there have been recent papers on ways to relax this assumption (see ...
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2 votes
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Propensity score matching in difference-in-differences

I have a data set in which I have treatment, event, and treatment*event vectors, along with other variable vectors that I have computed. I ran my regressions and find my coefficients and their ...
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Difference-in-Difference with temporary event

I am running a Diff-in-Diff analysis about the triggering of a policy that once triggered bans a certain action for 6 months. I have run the analysis considering only pre and post period, including in ...
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In a differences in differences model with continuous treatment, what is the parallel trends assumption?

How is there a parallel trends assumption if there is no formally defined treatment group?
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Testing Difference in Difference Assumptions in Panel Data

In the DiD analysis there are 3 main assumptions that should be respected (as far as I know): parallel trend positivity exchangeability MY DATA: I have a 2-year panel data containing data for $705$ ...
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Parallel Trend assumption in DiD

This assumption should rule out the concern of selection bias, right? For example, I am looking at the effect of increasing police presence on crimes. The government decided to put more police in ...
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Interpreting parallel trends (Diff-in-Diff)

I am evaluating the impact of a capital gains tax hike that was implemented in certain states, but not others, using a Diff-in-Diff method. However, I am not sure how to define my treatment time, and ...
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How is Jack & Suri's (2014) study a difference in difference model?

I have a question about a study that I want to replicate, namely the study Jack & Suri (2014): 'Risk Sharing and Transactions Costs: Evidence from Kenya’s Mobile Money Revolution' (available here: ...
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Clarifying confusion in heterogeneous teatment of staggered Difference-in-Differences estimator?

In a post previously, I have asked about whu=y the weight is negative and got an excellent answer. But now, when I reread it, I thought that I did not fully understand the answer and I think the ...
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