Due to the inherent subjectivity and poor definition of the task, mentioned above, it is difficult for annotators to reliably produce these annotations (Bryant and Ng, 2015).
this requirement can be relinquished by treating GEC as a text-to-text rewriting task and borrowing metrics from machine translation, as Park and Levy (2011) did with BLEU (Papineni et al., 2002) and METEOR (Lavie and Agarwal, 2007).