Counterfactual Learning to Rank (LTR) methods optimize ranking systems using
logged user interactions that contain interaction biases. Existing methods are
only unbiased if users are presented with all relevant items in every ranking.
There is currently no existing counterfactual unbiased LTR method for top-k
rankings. We introduce a novel policy-aware counterfactual estimator for LTR
metrics that can account for the effect of a stochastic logging policy. We
prove that the policy-aware estimator is unbiased if every relevant item has a
non-zero probability to appear in the top-k ranking. Our experimental results
show that the performance of our estimator is not affected by the size of k:
for any k, the policy-aware estimator reaches the same retrieval performance
while learning from top-k feedback as when learning from feedback on the full
ranking. Lastly, we introduce novel extensions of traditional LTR methods to
perform counterfactual LTR and to optimize top-k metrics. Together, our
contributions introduce the first policy-aware unbiased LTR approach that
learns from top-k feedback and optimizes top-k metrics. As a result,
counterfactual LTR is now applicable to the very prevalent top-k ranking
setting in search and recommendation.

本文介绍的计数事实学习 (LTR) 方法，使用包含交互偏差的已记录的用户交互来优化排名系统，通过引入一种新的策略感知的计数事实估计器，该方法可以适应随机记录策略的影响。同时，本文中还提出了一些传统 LTR 方法的新扩展方法，用于执行计数事实 LTR 并优化 top-k 评估指标，这些贡献介绍了首个可以应用于搜索和推荐中的非偏置 LTR 方法。