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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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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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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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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 ...
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Pre- Post comparisons for Difference-in-Differences

I have a panel structure with with three periods: pre, during, and post treatment. There are two ways running the DID approach: 1- The first one is to run one DID regression as the answer show in the ...
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Statistics of Diff in diff with optimal group

I am trying to run a diff in diff to measure the impact of a feature. I want to run the experiment per geo region and I have 90 regions. To run a proper diff in diff I should split in have the ...
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Interpreting Triple Difference coefficient with dummy variable

In my paper, I have estimated a triple difference-in-difference model where the outcome variable is a dummy variable indicating if the given individual is employed or not. Let's say that policy that I ...
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How to do PSM with panel data using PanelMatch?

I would greatly appreciate if you could let me know how to use PanelMatch for my dataset. Unfortunately, I couldn't find it's manual so I don't know how to find which firms are matched, how to extract ...
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Shortfalls of using Machine Learning algorithms to predict counterfactual outcome of the treated

To see the effect of a treatment we would like to know the difference between a person in a world in which she received the treatment and one in which she does not. Since we never observe the ...
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DiD with 2 time periods but multiple entities

How does DiD work for multiple entities but only 2 time periods? Would you still use panel data and which regression would you run? Thank you in advance
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DiD Different Scenarios

I have a few questions about DiD and impact of changing minimum wages on employment. a) Have 2 states, 1 changes min wage and 1 doesnt, and 2 time periods so can easily compute this using a simple ...
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Difference-in-Differences combining 3 periods prior to, during and after treatment

I have Difference-in-Differences models with 3 periods: pre-treatment, treatment and post-treatment periods. Normally, we could do DID in the following way: run DID between pre-treatment and ...
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Can I use a first difference variable as dependent variable in a panel regression even if it contains both positive and negative values?

Can I still use a first difference variable as the outcome variable to run a panel (say, diff-in-diff) regression? For example, my dependent variable is defined as $Y_{i,t} = M_{i,t} - M_{i,t-1} - P_{...
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Placebo Tests: Is it okay to create a placebo treatment group from a random sample of the control group?

I am running a 2 period difference in differences model on a repeated cross section. I want to test the parallel trend assumption using a placebo test. I have read that to do this "you perform an ...
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What does “randomly assigned conditional on some observable” mean intuitively?

From my textbook it say that "If the treatment in a quasi-experiment is "as if" randomly assigned, conditional on some observed variables w, then the treatment effect can be estimated using ...
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Matching on pre-treatment outcome in diff-in-diff

The parallel trends assumption for a difference-in-differences analysis does not require the level of the trends to be similar (just parallel). However, in a case where we want the levels to be ...
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Difference-in-differences using two time series

I hope the group will be able to help on the following. I have the following policy-evaluation problem: stock exchange A reduced their trading costs after period X (say, after 2008), thus managing to ...
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Using difference-in-differences as data preprocessing

I am having difficulties with wrapping my head around an idea. Can difference-in-differences be used to remove bias from the data? I found a mention here: "Difference in differences is a well-accepted ...
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Is it possible to add the standard errors of 2 groups together to obtain the standard error of the 2 groups combined

I am trying to recreate the results in this table. The results have been obtained by difference in difference estimation. I can obtain values from all columns except for column 5 and 6. Column 5 says ...
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Difference-in-differences with unbalanced panel data

I am working on a quasi-experimental study with a large unbalanced panel dataset. There are N=300,000 and T=20, where roughly 50,000 individuals receive treatment since several different periods. I ...
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why did Meyer use difference in difference to estimate the impact of workers compensation on injury duration?

Meyer, Viscusi and Durbin (MVD) measured the impact of increases in workers compensation on the amount of time a person would stay out of work if they were injured. They say in the paper that benefits ...
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53 views

Diff-in-diff with mactched control group

I want to run a diff-in-diff model. To choose an appropriate control group, I use a nearest-neighbor matching model based on several determinants of the outcome variable that I study. I was ...
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pospensity score modeling with differences in differences

I want to use a difference in differences specification which groups the data together using propensity scores. To do this is it as simple as obtaining the propensity scores, then taking the ...
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How do I code and analyze more than one set of treatments (e.g., intervention, implementation) within Difference-in-differences analysis?

I am working on a project in which I want to utilized difference-in-differences (DID) analysis to look at the impact of a county-level policy on rates of a social problem at the county level in a ...
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1answer
116 views

Diff-in-Diff with multiple treatment groups

I have monthly panel data and I want to estimate the effects of two different treatments that occur in different time periods. The treatment groups are not the same. An individual can belong one, both ...
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common trend test-coefficient plot

I'm doing the common trend test for DID, and want to use "coefplot" to make a coefficient plot, but I don't know how to show the last pre-treatment period(coefficient is zero) on the plot, since this ...
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Can I use an instrumental variable to control for treatment endogeneity in differences-in-differences model?

I have panel data with two time periods (pre and post) and two groups (treatment and control). I have a differences-in-differences model with the standard estimating equation: \begin{equation} y_{it} ...
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Diff-in-Diff special type of OLS?

Is difference-in-differences just a special type of OLS? Can I add fixed effects in my diff-in-diff model?
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Diff in diff model with multiple treatments in multiple perdiods?

Can I estimate a diff in diff model to compare the effects of two different treatments that apply in different time periods in different countries? I have 30 countries for an average time span of 34 ...