In a seminal paper Abadie, Diamond, and Hainmueller [2010] (ADH), see also
Abadie and Gardeazabal [2003], Abadie et al. [2014], develop the synthetic
control procedure for estimating the effect of a treatment, in the presence of
a single treated unit and a number of control units, with pre-treatment
outcomes observed for all units. The method constructs a se