Synth is a package for R that enables one to construct a synthetic control group.
It constructs a synthetic control group based both on predictors, and on the dependent variable.
synth constructs this synthetic control group by searching for a weighted combination of control units chosen to approximate the unit affected by the intervention in terms of characteristics that are predictive of the outcome.
However, in my case, I am trying to estimate a difference-in-differences model without any predictors used as controls.
Hence, I have only one variable (the total amount of accidents in a city, in my case). I need to find the combination of control-groups that would resemble the treatment group in term of this variable only.
Is it possible to implement it using the Synth package?