SynthControl.jl
Julia package for synthetic control methods
The package is currently at alpha stage - it currently offers a basic SyntheticControlModel
implementation which uses all pre-treatment periods and no other covariates in constructing the
control unit.
Installation
The package is registered in the general registry, installation therefore works through the Pkg REPL
pkg> add SynthControl
Usage
Fitting a SimpleSCM model
The package includes example data borrowed from the CER Brexit study:
julia> using SynthControl, Dates
julia> df = load_brexit()
897×3 DataFrame
│ Row │ country │ quarter │ realgdp │
│ │ String │ Date │ Float64 │
├─────┼────────────────┼────────────┼─────────┤
│ 1 │ Australia │ 2009-01-01 │ 1.04 │
│ 2 │ Austria │ 2009-01-01 │ -1.53 │
│ 3 │ Belgium │ 2009-01-01 │ -1.15 │
⋮
│ 894 │ Sweden │ 2018-07-01 │ 22.48 │
│ 895 │ Switzerland │ 2018-07-01 │ 14.35 │
│ 896 │ United Kingdom │ 2018-07-01 │ 15.72 │
│ 897 │ United States │ 2018-07-01 │ 19.32 │
The package defines a SimpleSCM type, instances of which can be constructed from a
TreatmentPanel object from the package
TreatmentPanels. The TreatmentPanel is
constructed from a DataFrame and a specification of treatment assignment. The SimpleSCM model
constructs a synthetic control unit based only
The example data set includes quarterly GDP for a number of OECD countries, and we are interested in estimating the impact of the Brexit vote in Q2 2016 on GDP in the UK:
julia> bp = BalancedPanel(df, "United Kingdom" => Date(2016, 7, 1); id_var = :country, t_var = :quarter, outcome_var = :realgdp)
Balanced Panel - single treated unit, continuous treatment
Treated unit: United Kingdom
Number of untreated units: 22
First treatment period: 2016-07-01
Number of pretreatment periods: 30
Number of treatment periods: 9
julia> s = SimpleSCM(bp)
Synthetic Control Model
Treatment panel:
Balanced Panel - single treated unit, continuous treatment
Treated unit: United Kingdom
Number of untreated units: 22
First treatment period: 2016-07-01
Number of pretreatment periods: 30
Number of treatment periods: 9
Model is not fitted
The output indicates that the model is not fitted, that is we have at this stage
only defined the basic model structure. We can fit the model using the fit!
function, which will modify our SimpleSCM in place:
julia> fit!(s)
Synthetic Control Model
Treatment panel:
Balanced Panel - single treated unit, continuous treatment
Treated unit: United Kingdom
Number of untreated units: 22
First treatment period: 2016-07-01
Number of pretreatment periods: 30
Number of treatment periods: 9
Model is fitted
Impact estimates: [-0.54, -0.31, -0.206, -0.732, -1.241, -1.482, -1.818, -2.327, -1.994]
The reported impact estimates are the difference between observed outcome variable and estimated outcome in the absence of treatment - a negative value therefore means the treatment is expected to have reduced the outcome variable compared to the counterfactual.
The package also defines a plot recipe which allows to visualise the estimated impact:
julia> using Plots
julia> plot(s_model)
Fitting a SyntheticDiD model
The package also implements a the synthetic differences-in-differences estimator of Arkhangelsky et
al. (2021) with the SyntheticDiD type. An example using data on German reunification:
julia> bp = load_germany_panel()
Balanced Panel - single treated unit, continuous treatment
Treated unit: West Germany
Number of untreated units: 16
First treatment period: 1990
Number of pretreatment periods: 30
Number of treatment periods: 14
Here we are using the load_*_panel() family of functions rather than the load_*() family of
functions used above - when using the panel version of the load functions, a BalancedPanel
object is returned which obviates the need for creating this from the raw data.
Fitting the model:
julia> sdid_model = SyntheticDiD(bp);
julia> fit!(sdid_model);
show and plot support is not yet implemented for SyntheticDiD models, but the point estimate
and standard error of the causal effect can be accessed directly from the model object:
julia> sdid_model.τ̂
1-element Vector{Float64}:
-3121.95256130856
julia> sdid_model.se_τ̂
1-element Vector{Float64}:
327.9157408571397