Recommender systems usually learn user interests from various user behaviors, including clicks and postclick behaviors (e.g., like and favorite, which reflects the true interests of users). However, these behaviors inevitably exhibit popularity bias, leading to some unfairness issues: 1) for items with similar quality, more popular ones get more exposure; and 2) even worse the popular items with lower popularity might receive more exposure. Existing work on mitigating popularity bias blindly eliminates the bias and usually ignores the effect of item quality. We argue that the relationships between different user behaviors (e.g., conversion rate) actually reflect the item quality. Therefore, to handle the unfairness issues, we propose to mitigate the popularity bias by considering multiple user behaviors. In this work, we examine causal relationships behind the interaction generation procedure in multibehavior recommendation. Specifically, we find that: 1) item popularity is a confounder between the exposed items and users' postclick interactions, leading to the exposure unfairness; and 2) some hidden confounders (e.g., the reputation of item producers) affect both item popularity and quality, resulting in the quality unfairness. To alleviate these confounding issues, we propose a causal framework to estimate the causal effect, which leverages <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">backdoor adjustment</i> to block the backdoor paths caused by the confounders. In the inference stage, we remove the negative effect of popularity and utilize the good effect of quality for recommendation. Experiments on two real-world datasets validate the effectiveness of our proposed framework, which enhances fairness without sacrificing recommendation accuracy on postclick behavior.

Causal Intervention for Fairness in Multibehavior Recommendation