Exemplar Guided Active Learning
This work addresses the challenge of label imbalance in NLP tasks like word sense disambiguation, offering a method to reduce annotation costs, though it is incremental as it builds on existing active learning and embedding techniques.
The paper tackles the problem of active learning for word sense disambiguation with imbalanced label distributions, aiming to efficiently identify and classify common classes while minimizing annotation of rare ones. It introduces an algorithm that leverages contextual embeddings and a stopping rule, proving logarithmic cost overhead and showing significant reductions in samples needed to achieve target accuracy in experiments.
We consider the problem of wisely using a limited budget to label a small subset of a large unlabeled dataset. We are motivated by the NLP problem of word sense disambiguation. For any word, we have a set of candidate labels from a knowledge base, but the label set is not necessarily representative of what occurs in the data: there may exist labels in the knowledge base that very rarely occur in the corpus because the sense is rare in modern English; and conversely there may exist true labels that do not exist in our knowledge base. Our aim is to obtain a classifier that performs as well as possible on examples of each "common class" that occurs with frequency above a given threshold in the unlabeled set while annotating as few examples as possible from "rare classes" whose labels occur with less than this frequency. The challenge is that we are not informed which labels are common and which are rare, and the true label distribution may exhibit extreme skew. We describe an active learning approach that (1) explicitly searches for rare classes by leveraging the contextual embedding spaces provided by modern language models, and (2) incorporates a stopping rule that ignores classes once we prove that they occur below our target threshold with high probability. We prove that our algorithm only costs logarithmically more than a hypothetical approach that knows all true label frequencies and show experimentally that incorporating automated search can significantly reduce the number of samples needed to reach target accuracy levels.