Cost-Sensitive BERT for Generalisable Sentence Classification on Imbalanced Data

Harish Tayyar Madabushi, Elena Kochkina, Michael Castelle


Abstract
The automatic identification of propaganda has gained significance in recent years due to technological and social changes in the way news is generated and consumed. That this task can be addressed effectively using BERT, a powerful new architecture which can be fine-tuned for text classification tasks, is not surprising. However, propaganda detection, like other tasks that deal with news documents and other forms of decontextualized social communication (e.g. sentiment analysis), inherently deals with data whose categories are simultaneously imbalanced and dissimilar. We show that BERT, while capable of handling imbalanced classes with no additional data augmentation, does not generalise well when the training and test data are sufficiently dissimilar (as is often the case with news sources, whose topics evolve over time). We show how to address this problem by providing a statistical measure of similarity between datasets and a method of incorporating cost-weighting into BERT when the training and test sets are dissimilar. We test these methods on the Propaganda Techniques Corpus (PTC) and achieve the second highest score on sentence-level propaganda classification.
Anthology ID:
D19-5018
Original:
D19-5018v1
Version 2:
D19-5018v2
Volume:
Proceedings of the Second Workshop on Natural Language Processing for Internet Freedom: Censorship, Disinformation, and Propaganda
Month:
November
Year:
2019
Address:
Hong Kong, China
Editors:
Anna Feldman, Giovanni Da San Martino, Alberto Barrón-Cedeño, Chris Brew, Chris Leberknight, Preslav Nakov
Venue:
NLP4IF
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
125–134
Language:
URL:
https://aclanthology.org/D19-5018
DOI:
10.18653/v1/D19-5018
Bibkey:
Cite (ACL):
Harish Tayyar Madabushi, Elena Kochkina, and Michael Castelle. 2019. Cost-Sensitive BERT for Generalisable Sentence Classification on Imbalanced Data. In Proceedings of the Second Workshop on Natural Language Processing for Internet Freedom: Censorship, Disinformation, and Propaganda, pages 125–134, Hong Kong, China. Association for Computational Linguistics.
Cite (Informal):
Cost-Sensitive BERT for Generalisable Sentence Classification on Imbalanced Data (Tayyar Madabushi et al., NLP4IF 2019)
Copy Citation:
PDF:
https://aclanthology.org/D19-5018.pdf