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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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Difference-in-difference (DD) estimator for non-discrete, longitudinal data?

There are many examples of how to set up a DD model for two points in time and with dummy variables (0s and 1s) separating the treated from control units and before and after intervention periods. ...
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Event Study: Event time coefficients vs post change coefficient

I have an event study regression with an unbalanced panel. I include unit and time fixed effects as well as a linear time trend control: $Y_{st} = \sum_{\tau \neq -1} \delta_{\tau} \mathbf{1}(YS_{st} ...
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How to test for a difference between differences?

I have 6 sites with 3 sites as constant food in a feeder and 3 sites as pulsed food in a feeder. For the pulsed food sites, there are days with food and without food.So, I have 2 treatments: constant, ...
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Regression model for difference-in-differences analysis with two post-periods

I'm attempting a difference-in-differences analysis with one pre-treatment time point (0), and two post-treatment time points (1, 2). I'd like to know, firstly, whether there's a significant ...
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Setting up fixed effect regression with specific baseline comparison group

I'd like to set up a fixed effects regression equation where the coefficients and standard errors can be interpreted to represent a specific comparison that I am interested in. That is, I want to ...
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Regressing the “fixed effect” on time invariant characteristics. Is it possible? [duplicate]

I would like to use estimations of "fixed effect" from my panel data model as a dependent variable and study whether this depends on time invariant characteristics. I've not been able to find an ...
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Difference-in-differences or something else? Regrouping after intervening event

I'm working on a project for my econometrics class and I could use some help. I'm looking at the effects of a Supreme Court decision, Tapia v. U.S, on the length of sentences handed out for drug ...
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Can you use difference in difference with a single group of individuals?

So I am looking at inheritances and how these could effect the labour supply choices of individuals. I have a variable where people state if they expect an inheritance or not. Now, I want to see if in ...
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how to regress for common trend assumption

I have a database of applicants for a grant and their applications for each year. I want to know the effect of the grant on nr of publications. But first i want to perform a common trend analysis. i ...
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Fixed effects DiD-Design

I am currently working on my master thesis and I am in the middle of my data cleaning up process. I am studying the effects of certain mergers during a sample period of 20 years. I use time fixed ...
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Comparative study using synthetic control

I am currently working on an idea for a paper and I've had an idea for a "new" methodology, but I am not sure if it's correct to apply such a method or if I should modify it in some way. Basically ...
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Log-linear difference-in-differences

I am estimating several linear models using a difference-in-differences (DiD) framework. The model interacts a treatment indicator (i.e., 1 for the treatment group, 0 for the control group) and a "...
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Time period for difference-in-differences analysis

Please, help me with the following issue. I want to analyze effect of firm location on its stock preformance (measure monthly) during the crisis. For this I construct the following dummies: Crisis = 1 ...
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How can I convert difference-in-differences to an effect size? [closed]

I haven't been able to find a good source on a way to convert the difference in differences to Cohen's D. The way I've been calculating the DD is: ...
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Corroborating a differnce in differences identification strategy

I read in Mostly harmless econometrics that a good way of testing whether a difference in differences is a good identification strategy is running this equation: where the first sums are post-...
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Does the difference in difference techniques assumes the dependent variable has a normal distribution?

I'm trying to estimate the effect of an event. The data I have is number of sales in 7 different periods of time (3 periods before the event, the period that the event happens and 3 periods after the ...
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Treatment effect (DID) heterogeneity conditional on a continous variable

as stated in the title, I'm thinking about exploring the heterogeneity of treatment effect result from a DID design based on a continuous variable. To be specific: \begin{align} & \mathrm{Profit}...
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Difference-in-difference: common trend

I'm new to this concept, and I'm referring to the book Mastering Metrics by Angrist. It states that an important assumption of Difference-in-Difference is the common trend assumption. I'm a little ...
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Improving a Difference-in-Differences Analysis of a Health Policy Intervention

I'm attempting a 'difference-in-differences' analysis of a health policy intervention, over 3 years. I'd appreciate advice on my methodology. Scenario: Year 0: Health clinics are given financial ...
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Parallel trend assumption in diff-in-diff and fixed effects models

What happens if the parallel trend assumption between control and treatment groups (diff-in-diff) or between individuals (individual-level fixed effects model) is not fulfilled?
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Standard Error/Confidence Intervals for a Difference-in-differences analysis

I'm attempting a 'difference-in-differences' analysis of a health policy intervention. Scenario: Health clinics are paid for the percentage of eligible patients who they give the right treatment to. ...
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Should I use a difference-in-difference method for migration flows and average unskilled worker incomes or a lagged DV?

I am using data from a variety of sources to measure if migration inflows lead to an increase in unskilled worker wages. I am controlling for number of illegal immigrants, migrant unemployment, etc. ...
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Difference-in-differences with individual-level panel data

Main Idea I want to estimate the effect of a treatment that affected a group of individuals that are scattered over a larger geographic area in a short matter of time (a week) via DID. I have reason ...
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Treatment effect estimation: year is treatment

I want to estimate the effect of tax increase on the consumption at the regional level. I have 100 regions in pre-treatment period (year 2010) and the same regions in post-treatment period (year 2011)....
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Synthetic Controls vs Coarsened Exact Matching with weights vs Coarsened Exact Matching k2k

My question is mostly out of curiosity. How one should choose between synthetic controls and coarsened exact matching (CEM) when he/she wants to combine it with difference-in-difference design? ...
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Specification of a difference-in-differences model in r

I am working through a difference-in-differences model. While I've learned a good deal browsing SE, I'd like to hear from someone more experienced with fixed effects if my model is correctly specified....
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Difference-in-Differences (DID) estimator with fertility data

In a nutshell, I'm using DID to estimate the impact of a cash-transfer program on fertility in a specific country. The program offers families an untaxed, unconditional cash transfer for every second ...
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Inclusion of Age^2 changes results completely

I'm running a diff-in-diff with model with years of education as an outcome variable. $Y_{it}=\beta_0+\beta_1Treat_i+\gamma_t+\beta_2Treat_{i}*Post_t+X'\gamma+\epsilon_{it}$ The treatment dummy is ...
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Difference-in-differences model with time-fixed effects only

Assume that we have a panel data set with individuals' income (Y) over multiple years and a certain event (POST) in one year that is hypothesized to affect Y for a subgroup of these individuals (TREAT)...
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A difference-in-differences propensity score matching approach

I am facing some challenges using the DID.I have around 500 Items off which 100 are test and its very difficult to find a control group for DID, so I used PSM to find control group using nearest ...
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Estimation of substitution effect

I have a market with three goods: PRODUCT_I,PRODUCT_II, PRODUCT_III. PRODUCT_I is banned by a policy, and its sales brought down to 0. I want to estimate to what extent PRODUCT_II and/or PRODUCT_III ...
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How do I cluster my standard errors in a triple differences approach with two clusters?

I am trying to estimate this following triple differences regression in order to test for parallel trends in the difference in differences: My treatment is binary (it is a law that was passed in one ...
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Difference-in-Difference model where treatment intensity increases over time

I'm currently trying to figure out whether a specific Diff-in-Diff model makes sense. Suppose I have a set of 20 countries, where one country (A) introduced a tax for a specific good in 2005 and ...
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Sample restriction in difference in difference: interpretation of the results and (potential) bias

Within a difference in difference (DD) strategy trends of an outcome of interest are compared for the treatment and the control groups before and after an intervention. The crucial assumption is that ...
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DiD estimator where all groups have some treatment

I am analysing some data on the impact of immigration on peoples attitudes to welfare. I wanted to use a difference in difference estimator as an exogenous shock caused immigration to drastically ...
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Heterogenous effects in DID models

I am working on a standard DID research design where all the assumptions are met - focused on a policy reform affecting a number of sectors in a country. I would like to improve the design by ...
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Propensity score matching and DD over different event windows

I'm currently working on a project in which we are trying to investigate the operating (accounting) performance of seasoned equity offerings. To comprehend the endogeneity problem, we apply ...
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How to handle a Difference-in-Difference situation where the control group has no pre or post period?

I am running the following DiD specification in Stata $ Ln(1+Activity)_{it}=α_0+ α_1 PreTreat_{i,t-3}+α_2 PreTreat_{i,t-2} + α_3 PreTreat_{i,t-1}\\+β_1 PostTreat_{i,t+1} +β_2 PostTreat_{i,t+2}+β_3 ...
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Estimate on constant in diff-in-diff estimation is off-the-charts big

I've estimated a diff-in-diff using Stata - very simple situation: y = b0 + b1 T + b2 P + b3 TxP + e T = 1 means treatment, 0 is control. P = 1 means post treatment, 0 is pre-treatment. Problem: ...
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Linear Regression: Calculating a treatment effect directly in regression vs. averaging potential outcomes

Suppose I have the following true model, where an individual $i$ at a particular point in time $t$ is either treated ($W=1)$ or untreated ($W=0$). The outcome for individual $i$ at time $t$ under ...
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DnD - Parallel trends in subgroups?

I am estimating a standard two period difference in differences model, where I estimate whether a policy change was associated with an individual level behavior change in a state that implemented it ...
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DiD test for one “period”

I am working with a model that calculates the values of stocks from S&P1500, the model then outputs the median of absolute errors between the estimate and the actual value. I've now tested the ...
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Comparing two difference-in-difference models when making the treatment group larger

I have a question regarding some potentially existing empirical tests in the difference-in-difference context. Assume that I have the usual setting of observing some hypothetical outcome for a ...
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Sample selection in difference-in-differences

I have a dependent variables with a significant amount of zeros (and the share of zeros is different between the control and treatment groups, and changes between the pre- and post-treatment periods). ...
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Spatial Temporal Autoregressive Regression and implication on Fixed effects assumption in Difference in Differences

I am currently planning on testing the effects of marginal price change of properties based on an exogenous event using Spatial DID model. The model has a spatio-temporal lagged variable (y) which ...
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45 views

Using propensity score matching to find control group for Diff-In-Diff

I am trying out DID as part of coming up with a model to estimate the effect. Below is the scenario: I have around 2000 items for test group(Item count may increase or decrease). Challenge is to find ...
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Dependent variable with many zeros in a difference-in-differences model

There is a question with a similar title: How do I estimate a differences in differences model when the dependent variable has many zeros? However, mine is a little different. Let's assume I have a ...
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Stata: Difference in Difference; common-trend plot [closed]

I estimate the following flexible difference-in-difference model with Stata: regress Y i.time i.time##i.treatment Starting from this model, I'd like to ...
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Difference-in-differences: selection bias due to availability of outcome data

I have run a diff-in-diff specification to evaluate the outcome of a policy on disease treatment rate, where those countries included in the policy form the intervention group and those excluded are ...
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24 views

Difference In Difference method : How to find control group

I am trying out DID as part of coming up with a model to estimate the effect. Below is the scenario: I have around 2000 items for test group(Item count may increase or decrease). Challenge is to find ...