Synthetic Control Methods for Comparative Case Studies: Estimating the Effect of California’s Tobacco Control Program

Building on an idea in Abadie and Gardeazabal (2003), this article investi- \ngates the application of synthetic control methods to comparative case studies. \nWe discuss the advantages of these methods and apply them to study the ef- \nfects of Proposition 99, a large-scale tobacco control program that California \nimplemented in 1988. We demonstrate that following Proposition 99 tobacco \nconsumption fell markedly in California relative to a comparable synthetic con- \ntrol region. We estimate that by the year 2000 annual per capita cigarette sales \nin California were about 26 packs lower than what they would have been in the \nabsence of Proposition 99. Using new inferential methods proposed in this ar- \nticle, we demonstrate the signi¯cance of our estimates. Given that many policy \ninterventions and events of interest in social sciences take place at an aggregate \nlevel (countries, regions, cities, etc.) and affect a small number of aggregate \nunits, the potential applicability of synthetic control methods to comparative \ncase studies is very large, especially in situations where traditional regression \nmethods are not appropriate.