“…Step 1: Compute the estimated projection direction̂[ ] by fitting a single-index model with "synthesis" data Cui, Härdle, and Zhu (2011);Li, Lai, and Lian (2015); Li, Peng, Dong, and Tong (2014); Lian, Liang, and Carroll (2015); Liang, Liu, Li, and Tsai (2010); Peng and Huang (2011);Yang, Tong, and Li (2019); Zhang, Feng, and Xu (2015); Zhang, He, Lu, and Wen (2018).…”