Furthermore, Martindale et al. [124] proposed a bag-of-vectors sentence similarity (BVSS) metric
for measuring sentence adequacy in machine translation, that only refers to the target text. This
statistical metric helps to determine whether the MT output has a different amount of information
than the translation reference.

Although simple and effective, one potential limitation of the lexical matching is that it can only

handle the lexical information. Thus, it fails to deal with syntactic or semantic variations [166].

2Note that PARENT is a general metric like ROUGE and BLEU, not only constrained to hallucination

ACM Comput. Surv., Vol. 1, No. 1, Article . Publication date: February 2022.

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Ziwei Ji, et al.
SurveyofHallucinationinNatural Language Generation