Following previous work (Zhang and Lapata, 2017;Zhao et al., 2018), we use SARI as our main automatic metric for evaluation (Xu et al., 2016).
11 SARI calculates how often a generated sentence correctly keeps, inserts, and deletes n-grams from the complex sentence, using the reference simple standard as the gold-standard, where 1 ≤ n ≤ 4.