USR: An Unsupervised and Reference Free Evaluation Metric for Dialog Generation Shikib Mehri author Maxine Eskenazi author 2020-07 text Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics Dan Jurafsky editor Joyce Chai editor Natalie Schluter editor Joel Tetreault editor Association for Computational Linguistics Online conference publication mehri-eskenazi-2020-usr 10.18653/v1/2020.acl-main.64 https://aclanthology.org/2020.acl-main.64/ 2020-07 681 707