Robust Educational Dialogue Act Classifiers with Low-Resource and Imbalanced Datasets
Dialogue acts (DAs) can represent conversational actions of tutors or
students that take place during tutoring dialogues. Automating the
identification of DAs in tutoring dialogues is significant to the design of
dialogue-based intelligent tutoring systems. Many prior studies employ machine
learning models to classify DAs in tutoring dialogues and invest much effort to
optimize the classification accuracy by using limited amounts of training data
(i.e., low-resource data scenario). However, beyond the classification
accuracy, the robustness of the classifier is also important, which can reflect
the capability of the classifier on learning the patterns from different class
distributions. We note that many prior studies on classifying educational DAs
employ cross entropy (CE) loss to optimize DA classifiers on low-resource data
with imbalanced DA distribution. The DA classifiers in these studies tend to
prioritize accuracy on the majority class at the expense of the minority class
which might not be robust to the data with imbalanced ratios of different DA
classes. To optimize the robustness of classifiers on imbalanced class
distributions, we propose to optimize the performance of the DA classifier by
maximizing the area under the ROC curve (AUC) score (i.e., AUC maximization).
Through extensive experiments, our study provides evidence that (i) by
maximizing AUC in the training process, the DA classifier achieves significant
performance improvement compared to the CE approach under low-resource data,
and (ii) AUC maximization approaches can improve the robustness of the DA
classifier under different class imbalance ratios.