BERTs of a feather do not generalize together: Large variability in generalization across models with similar test set performance
This reveals high variability in generalization among models with similar test performance, highlighting a problem for reliability in NLP applications.
The study investigated whether multiple instances of BERT fine-tuned on the same dataset make similar linguistic generalizations, finding that while test set performance was consistent (83.6-84.8% accuracy), generalization on syntactic tasks varied widely, with accuracy ranging from 0.00% to 66.2% for subject-object swaps.
If the same neural network architecture is trained multiple times on the same dataset, will it make similar linguistic generalizations across runs? To study this question, we fine-tuned 100 instances of BERT on the Multi-genre Natural Language Inference (MNLI) dataset and evaluated them on the HANS dataset, which evaluates syntactic generalization in natural language inference. On the MNLI development set, the behavior of all instances was remarkably consistent, with accuracy ranging between 83.6% and 84.8%. In stark contrast, the same models varied widely in their generalization performance. For example, on the simple case of subject-object swap (e.g., determining that "the doctor visited the lawyer" does not entail "the lawyer visited the doctor"), accuracy ranged from 0.00% to 66.2%. Such variation is likely due to the presence of many local minima that are equally attractive to a low-bias learner such as a neural network; decreasing the variability may therefore require models with stronger inductive biases.