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.
721
questions
1
vote
0
answers
5
views
I want to determine the impact of a policy on carbon emissions in a single country by doing difference in difference but don't have a control group
The policy was implemented all over the country and applies to everyone. Can I do difference in difference looking at yearly total emissions data of the country before the policy was implemented vs ...
- 11
0
votes
0
answers
6
views
Difference-in-difference with border areas: how to create indicator for matched area?
I'm trying a DiD by comparing adjacent districts which lie on two sides of state border, before and after a policy. The scheme is following: state A introduced a policy in year t, while state B (...
- 1
0
votes
0
answers
15
views
How to interpret coefficient plots for a dynamic difference in differences model?
I know parallel trends assumption (PTA) is essential to a simple difference in difference model. Is it also true for the case of dynamic difference in difference model? For example, in the following ...
- 305
0
votes
0
answers
14
views
How to measure ATE on panel data with heterogeneous treatment effects and many treatments?
I want to measure the average effect of treatment D1 on money using a panel date like the one in the table below, with several units measured at different time periods, and either being treated more ...
1
vote
0
answers
14
views
Difference in Difference and Random Treatment Timing
I have a question about Difference-in-Difference estimation. It is well-known that the key identification assumption in Diff-in-Diff is the parallel trends assumption that says that in the absence of ...
- 151
1
vote
0
answers
10
views
Can I still call this as a difference-in-difference analysis?
I have a regression which has treatment and control groups.
I want to test how the treatment group (binary variable) reacts during crises periods compared to control group.
The crisis variable is a ...
- 444
0
votes
0
answers
21
views
Test the parallel trend assumption in DiD regression with controls
I am running a DiD regression to evaluate the effect of a policy and I want to check whether the parallel trend assumption holds in my data. However, the model includes control variables that can ...
- 1
0
votes
0
answers
7
views
Self-selection bias in difference-in-difference estimation
I am hoping to estimate the causal effects of a voluntary employment scheme available for U25 on mental health and financial independence using a difference-in-difference approach (DiD). Because ...
- 1
1
vote
1
answer
24
views
Which test can I use to test a difference in increase?
Let's say that medication A significantly increased the patients' health on average, but so did medication B (for independent sets of patients).
Obviously both medications increased the health of the ...
- 23
2
votes
0
answers
21
views
Difference in difference regression after propensity score matching
I’m doing some matching followed by difference-in-difference regression to look at the impact of a certain disease on people's income. The matching is done, and I’m preparing to go into the next stage,...
- 21
0
votes
0
answers
7
views
Does the scale of a control variable matter?
why does the effect of a control variable on the coefficient of interest depends on how the control variable is measured?
The following DiD model is estimated:
Y = beta_1Treat + beta_2Post + beta_3(...
- 1
0
votes
0
answers
24
views
Difference-in-differences with monthly data where the previous untreated year is used as the control group
I recently came across a setup of differences-in-differences which I have previously wondered about, but had not seen before in a published study. Consider the following setting:
Outcome: measured at ...
- 1
1
vote
1
answer
32
views
How to determine effect size confidence interval in a difference-of-differences A/B test
This seems like it should be a really simple thing, so I apologize if this has been answered elsewhere, but I've browsed dozens of existing questions and none seem to fit exactly.
Suppose I have two ...
- 11
0
votes
0
answers
7
views
Keep time invariant variables in difference-in-difference models
I want to run a difference-in-difference model to investigate the location of agricultural investments based on election outcomes. I assume that districts that voted for the local goverment receive ...
- 13
0
votes
1
answer
15
views
Parallel trend analysis in a two period panel data
I have a dataset , which is in panel nature for two time periods. I would like to whether it is possible to perform a DID analysis, and if yes is it possible to do a parallel trend analysis for only ...
- 11
0
votes
0
answers
21
views
Dynamic Treatment Effects for Difference in Differences / treatment effect by year / longterm treatment effects
how you would implement a dynamic treatment effect model for diff in diff in stata? I tried it for my setup and the results make no sense.
What I have done (2005 first treatment year):
centered the ...
- 1
0
votes
0
answers
8
views
How would you test for parallel trends in a panel data set of 2 time periods under DDD framework?
Suppose i have a panel data with 2 time periods (pre and post events), how would i test for parallel trends assumption under a DDD framework?
- 11
0
votes
0
answers
12
views
Difference in differences regression with multiple control/treatment pairs and time periods
I want to measure the effect of reporting CO2 emissions on stock returns. To do this, I am thinking of identifying natural experiments/events to study this effect.
My plan is to first identify stock ...
0
votes
0
answers
29
views
Difference-in-difference: how to integrate different types of treatment at different time points
I have a control group and treatment group and the treatment is introduced in the second phase after time point t. But the treatment can be different types at ...
- 263
0
votes
0
answers
36
views
Can I use DiD for a RDD design? (treatment determined by threshold)
is it possible to apply a Difference-in-Differences method for a quasi-experiment that determines treatment by a threshold? All schools below a certain API rank are treated the rest is not (control). ...
- 1
0
votes
0
answers
10
views
Questions on Difference in difference and statistical significance with aggregated data
Given that we usually have sample data, it makes sense to describe statistical significance in relation to the size of our sample and so on. But with, for example, country-level data, we might have a ...
- 11
0
votes
0
answers
18
views
Is there a method that can balance on two treatment?
I am regressing an outcome on two treatments using differences in differences.
To deal with the pre-trend problem, I introduced some balancing method and run the regression separately on either ...
- 15
0
votes
1
answer
51
views
Diff diff regression or regular linear regression
Let's say that we are trying to estimate the effect of a policy whose goal is to increase voter turnout in city-level elections (say, get out and vote campaigns ran by local government). Cities held ...
- 31
4
votes
2
answers
69
views
What are the differences between diff-in-diff and Fixed-Effects model?
I am trying to understand the differences in estimating diff-in-diff in different formulations. To exemplify, I'm using data from Abadie, et al., (2010), in which the authors estimate the effect of a ...
- 345
0
votes
0
answers
26
views
t-test on the difference-in-difference
I have sampled two groups with different means before treatment. Would it be possible to run a $t$-test after the treatment to see if the original difference between the means changed? Most of what I ...
- 13
0
votes
0
answers
38
views
Replicate a RDD study with a DiD
I am master student and new in this field.
I would like to replicate a study that uses a threshold for treatment to estimate the causal effect of X on Y. Consequently, in the original paper the RDD ...
- 1
0
votes
0
answers
26
views
Multiple treatment dynamic diff-in-diff
I have a question regarding the question here. In @Thomas Bilach answer, he gives the following example, which I have edited a bit more to add my own hypothetical examples:
$$
\begin{array}{ccc}
item ...
- 827
1
vote
0
answers
11
views
In my DiD regression, I have % change as dependent variable and log(x) as a regressor. How do I interpret the beta coefficient?
I am trying to study how rent changes has evolved over distance to the city center between the pre- and post-COVID time periods. So I devote particular focus on comparing the relative rental and house ...
1
vote
0
answers
26
views
Triple Difference (DDD) - Power Calculation Formula
I would like to conduct power analyses related to an experiment conducted under a triple difference estimation strategy. However, it doesn't seem like there is a lot written on this subject. Ideally, ...
- 527
2
votes
1
answer
74
views
Unit/individual fixed effects vs. group fixed effects in a causal setting (DiD, RCT, etc.)
I noticed that in difference-in-differences (DiDs), group fixed effects (FE) are predominantly used over unit/individual FE:
$$Y_{ist}=\alpha_s+\gamma_t+\delta D_{st}+\varepsilon_{ist}$$
What I don't ...
- 45
1
vote
1
answer
35
views
How do I estimate the Average Treatment Effect on the Treated in a Difference-In-Difference Model?
Suppose the DID model is
Y = a + b(Treatment) +c(Time) + d(Treatment*Time). Now, If i wanted to find out the average treatment effect on the treated, how should i modify my model?
- 11
1
vote
0
answers
14
views
Meta-analysis for studies with both baseline and follow-up measurements in both control and experimental groups
I am new to meta-analysis. I did a quick search, and I think I can wrap my mind around generating cohen's d and its variance when there is only a single distribution for each of the control group (C) ...
- 281
1
vote
1
answer
33
views
Differences-in-Differences Parallel Trends
I want to measure whether the impact of a company's headquarter country on my dependent variable (goodwill paid) is stronger during recessions. After some researching, I found out that the differences-...
- 11
0
votes
0
answers
21
views
Difference-in-Difference: What to do with control observations when there are multiple possible intervention periods
I have several years worth of individual level data on several thousand individuals and a corresponding measure. During those years several hundred individuals underwent an intervention with the hope ...
0
votes
0
answers
17
views
About fixed effects in DiD
Why do we need to control state-fixed effects in a Difference in Difference model? If we are comparing the difference in the change between post and pre-periods, then the fixed effects are naturally ...
1
vote
1
answer
34
views
Valid to run post-hoc tests on matched data or running afoul of Table 2 Fallacy?
After completing a difference-in-differences matched cohort analysis to estimate the pre/post treatment effect of a home health nursing intervention compared to a control group, my employers are ...
- 5,282
2
votes
0
answers
23
views
Appropriate fixed effect and clustered standard error to use in a diff-in-diff set up
My question is about using fixed effects and clustered standard errors in a difference-in-difference setup.
I am trying to estimate the causal effect of a policy change on a measure of employment over ...
- 21
1
vote
0
answers
47
views
Difference-in-differences approach for the units that are in the treatment and control group at the same time
I am trying to estimate a policy effect on farmers' land sizes. The policy (treatment) is at the village level. I could simply use a diff-in-diff approach by comparing farmers' lands across treatment ...
- 11
1
vote
0
answers
14
views
Members in treatment group serve as controls for other treatment members to eliminate unmeasured confounders in pre/post observational study?
Consider a typical observational healthcare study where pre/post health outcomes among patients receiving a treatment or care program are compared to a counterfactual control group who didn't receive ...
- 5,282
0
votes
0
answers
24
views
When should we expect WLS to be superior to OLS?
My question is motivated by this paper. In a nutshell, they are proposing an Diff-in-diff estimator that is estimated via WLS and should be superior to the classical one, estimated via OLS.
In this ...
- 345
0
votes
0
answers
16
views
Difference-in-differences with distance sensitive treatment effect
I want to use the difference-in-difference method to estimate the effect of treatment at multiple distances to the treatment location. I have a house price dataset from 2000 to 2020 and a public ...
- 1
3
votes
0
answers
79
views
Is difference-in-differences dead?
There have been a number of papers over the past 40 years supporting either change score or regressor analysis for longitudinal observational studies.
However, recent papers (for example, Tennant et ...
- 5,282
0
votes
0
answers
27
views
Difference in Differences with binary outcome and repeated cross section
I have to do a public policy evaluation (on R) based on an article where the authors use a quarterly survey to study the effect of a parental leave reform in 2015(reducing the length of leave) on the ...
- 1
0
votes
0
answers
23
views
Average Causal Response Difference-in-Difference with multiple time periods
I want to estimate the average causal response of a continuous treatment using DiD, with a balanced panel of units observed in 3 periods:
1st period: no one receives treatment
2nd period: some ...
- 11
2
votes
1
answer
111
views
Difference-in-differences with two treatments
I have two groups.
Group 1 received intervention A and Group 2 received intervention B. I'm interested in seeing if intervention A is more effective than intervention B. People cannot be enrolled in ...
- 23
0
votes
0
answers
29
views
Difference-in-differences estimation using using Weighted Regression
I am trying to estimate a diff-in-diff model by demeaning data and consider unit weights. To better explain, I'll show my understandings so far. Questions in bold.
Consider the classic diff-in-diff ...
- 345
0
votes
0
answers
15
views
What is most appropriate Difference in Difference estimator for controlling time varying covariates except TWFE
Due to limitations of two way fixed effects model in staggered settings. What is the most appropriate Difference in Difference estimator for controlling time varying observed confounders/covariates. ...
- 11
1
vote
0
answers
15
views
correlation effect of additional variable on the interaction term in multiple linear regression model
When we have the following two models:
$$A: y=\tilde\beta_0+\tilde\beta_1x_1+u$$
$$B: y=\hat\beta_0+\hat \beta_1x_1+\hat\beta_2x_2+v$$
We know $$\tilde \beta_1=\hat\beta_1+\hat\beta_2\tilde \delta_1$$ ...
- 305
1
vote
1
answer
41
views
Consequences (and Solutions) of Violating SUTVA in a DID Design
Using a difference-in-differences design, what are the consequences of violating the Stable Unit Treatment Value Assumptions (SUTVA)? I ask this because, in my specific field of research (conflict and ...
- 427
0
votes
0
answers
8
views
For a difference in difference, to identify the effect of treatment on the outcome, what is the necessary assumption in terms of potential oucomes?
I guess the most necessary assumption would be the parallel trend. The point is how to express it mathematically in terms of potential outcomes?
- 1