  Stance detection models may tend to rely on dataset bias in the text part as
a shortcut and thus fail to sufficiently learn the interaction between the
targets and texts. Recent debiasing methods usually treated features learned by
small models or big models at earlier steps as bias features and proposed to
exclude the branch learning those bias features during inference. However, most
of these methods fail to disentangle the ``good'' stance features and ``bad''
bias features in the text part. In this paper, we investigate how to mitigate
dataset bias in stance detection. Motivated by causal effects, we leverage a
novel counterfactual inference framework, which enables us to capture the
dataset bias in the text part as the direct causal effect of the text on
stances and reduce the dataset bias in the text part by subtracting the direct
text effect from the total causal effect. We novelly model bias features as
features that correlate with the stance labels but fail on intermediate stance
reasoning subtasks and propose an adversarial bias learning module to model the
bias more accurately. To verify whether our model could better model the
interaction between texts and targets, we test our model on recently proposed
test sets to evaluate the understanding of the task from various aspects.
Experiments demonstrate that our proposed method (1) could better model the
bias features, and (2) outperforms existing debiasing baselines on both the
original dataset and most of the newly constructed test sets.
