The R package Synth implements synthetic control methods for comparative case studies designed to estimate the causal effects of policy interventions and other events of interest (Abadie and Gardeazabal 2003; Abadie, Diamond, and Hainmueller 2010). These techniques are particularly well-suited to investigate events occurring at an aggregate level (i.e., countries, cities, regions, etc.) and affecting a relatively small number of units. Benefits and features of the Synth package are illustrated using data from Abadie and Gardeazabal (2003), which examined the economic impact of the terrorist conflict in the Basque Country.
Abadie, Alberto, Alexis Diamond and Jens Hainmueller. "Synth: An R Package for Synthetic Control Methods in Comparative Case Studies." Journal of Statistical Software 42.13 (June 2011): 1-17.