synthetic control incrementality test

Using Synthetic Controls:
Feasibility, Data Requirements, and Methodological Aspects

incrementality test的主要目的：( measure the incrementality of main metrics)
1\ allocate每个Chanel对acquire new customer的贡献
2\ 计算non-testing peroid的main metric multiple
3\ 常用公式 ：
  m u l t i p l e = s i t e o n − s i t e o f