On the Evaluation Metrics for Paraphrase Generation

In this paper we revisit automatic metrics for paraphrase evaluation and obtain two findings that disobey conventional wisdom: (1) Reference-free metrics achieve better performance than their reference-based counterparts. (2) Most commonly used metrics do not align well with human annotation. Underlying reasons behind the above findings are explored through additional experiments and in-depth analyses. Based on the experiments and analyses, we propose ParaScore, a new evaluation metric for paraphrase generation. It possesses the merits of referencebased and reference-free metrics and explicitly models lexical divergence. Based on our analysis and improvements, our proposed reference-based outperforms than referencefree metrics. Experimental results demonstrate that ParaScore significantly outperforms existing metrics. Our codes and toolkit are released in https://github.com/ shadowkiller33/ParaScore .