Regression Compatible Listwise Objectives for Calibrated Ranking
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As Learning-to-Rank (LTR) approaches primarily seek to improve ranking quality, their output scores are not scale-calibrated by design – for example, adding a constant to the score of each item on the list will not affect the list ordering. This fundamentally limits LTR usage in score-sensitive applications. Though a simple multi-objective approach that combines a regression and a ranking objective can effectively learn scale-calibrated scores, we argue that the two objectives can be inherently conflicting, which makes the trade-off far from ideal for both of them. In this paper, we propose a novel regression compatible ranking (RCR) approach to achieve a better trade-off. The advantage of the proposed approach is that the regression and ranking components are well aligned which brings new opportunities for harmonious regression and ranking. Theoretically, we show that the two components share the same minimizer at global minima while the regression component ensures scale calibration. Empirically, we show that the proposed approach performs well on both regression and ranking metrics on several public LTR datasets, and significantly improves the Pareto frontiers in the context of multi-objective optimization. Furthermore, we evaluated the proposed approach on YouTube Search and found that it not only improved the ranking quality of the production pCTR model, but also brought gains to the click prediction accuracy.
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