Causal relationship extraction from biomedical text using deep neural models: A comprehensive survey.

The identification of causal relationships between events or entities within biomedical texts is of great importance for creating scientific knowledge bases and is also a fundamental natural language processing (NLP) task. A causal (cause-effect) relation is defined as an association between two events in which the first must occur before the second. Although this task is an open problem in artificial intelligence, and despite its important role in information extraction from the biomedical literature, very few works have considered this problem. However, with the advent of new techniques in machine learning, especially deep neural networks, research increasingly addresses this problem. This paper summarizes state-of-the-art research, its applications, existing datasets, and remaining challenges. For this survey we have implemented and evaluated various techniques including a Multiview CNN (MVC), attention-based BiLSTM models and state-of-the-art word embedding models, such as those obtained with bidirectional encoder representations (ELMo) and transformer architectures (BioBERT). In addition, we have evaluated a graph LSTM as well as a baseline rule based system. We have investigated the class imbalance problem as an innate property of annotated data in this type of task. The results show that a considerable improvement of the results of state-of-the-art systems can be achieved when a simple random oversampling technique for data augmentation is used in order to reduce class imbalance.