# synthdid

**Repository Path**: econometric/synthdid

## Basic Information

- **Project Name**: synthdid
- **Description**: Synthetic difference in differences


- **Primary Language**: Unknown
- **License**: BSD-3-Clause
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 1
- **Created**: 2021-12-22
- **Last Updated**: 2023-05-26

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# synthdid: Synthetic Difference in Differences Estimation

[![Build Status](https://dev.azure.com/grf-labs/synth-inference/_apis/build/status/synth-inference.synthdid?branchName=master)](https://dev.azure.com/grf-labs/synth-inference/_build/latest?definitionId=4&branchName=master)

This package implements the synthetic difference in difference estimator (SDID) for the average treatment effect in panel data,
as proposed in Arkhangelsky et al (2019). We observe matrices of outcomes Y and binary treatment indicators W
that we think of as satisfying Y<sub>ij</sub> = L<sub>ij</sub> + &tau;<sub>ij</sub> W<sub>ij</sub> + &epsilon;<sub>ij</sub>.
Here &tau;<sub>ij</sub> is the effect of treatment on the unit i at time j, and we estimate the average effect of
treatment when and where it happened: the average of &tau;<sub>ij</sub> over the observations with W<sub>ij</sub>=1.
All treated units must begin treatment simultaneously, so W is a block matrix: W<sub>ij</sub> = 1 for i > N<sub>0</sub> and j > T<sub>0</sub>
and zero otherwise, with N<sub>0</sub> denoting the number of control units and T<sub>0</sub> the number of observation times
before onset of treatment. This applies, in particular, to the case of a single treated unit or treated period.


This package is currently in beta and the functionality and interface is subject to change.

Some helpful links for getting started:

- The [R package documentation](https://synth-inference.github.io/synthdid/) contains usage examples and method reference.
- The [online vignettes](https://synth-inference.github.io/synthdid/articles/more-plotting.html) contains a gallery of plot examples.
- For community questions and answers around usage, see [Github issues page](https://github.com/synth-inference/synthdid/issues).

### Installation

The current development version can be installed from source using devtools.

```R
devtools::install_github("synth-inference/synthdid")
```

### Example

```R
library(synthdid)

# Estimate the effect of California Proposition 99 on cigarette consumption
data('california_prop99')
setup = panel.matrices(california_prop99)
tau.hat = synthdid_estimate(setup$Y, setup$N0, setup$T0)
se = sqrt(vcov(tau.hat, method='placebo'))
sprintf('point estimate: %1.2f', tau.hat)
sprintf('95%% CI (%1.2f, %1.2f)', tau.hat - 1.96 * se, tau.hat + 1.96 * se)
plot(tau.hat)
```

#### References
Dmitry Arkhangelsky, Susan Athey, David A. Hirshberg, Guido W. Imbens, and Stefan Wager.
<b>Synthetic Difference in Differences</b>, 2019.
[<a href="https://arxiv.org/abs/1812.09970">arxiv</a>]