Beyond Movie Recommendations: Solving the Continuous Cold Start Problem in E-commerce Recommendations
by Julia Kiseleva, Alexander Tuzhilin, Jaap Kamps, Melanie Mueller, Lucas Bernardi, Chad Davis, Ivan Kovacek, Mats Stafseng Einarsen, Djoerd Hiemstra
Many e-commerce websites use recommender systems or personalized rankers to personalize search results based on their previous interactions. However, a large fraction of users has no prior interactions, making it impossible to use collaborative filtering or rely on user history for personalization. Even the most active users may visit only a few times a year and may have volatile needs or different personas, making their personal history a sparse and noisy signal at best. This paper investigates how, when we cannot rely on the user history, the large scale availability of other user interactions still allows us to build meaningful profiles from the contextual data and whether such contextual profiles are useful to customize the ranking, exemplified by data from a major online travel agent Booking.com.
Our main findings are threefold: First, we characterize the Continuous Cold Start Problem (CoCoS) from the viewpoint of typical e-commerce applications. Second, as explicit situational context is not available in typical real world applications, implicit cues from transaction logs used at scale can capture essential features of situational context. Third, contextual user profiles can be created offline, resulting in a set of smaller models compared to a single huge non-contextual model, making contextual ranking available with negligible CPU and memory footprint. Finally we conclude that, in an online A/B test on live users, our contextual ranker increased user engagement substantially over a non-contextual baseline, with click-through-rate (CTR) increased by 20%. This clearly demonstrates the value of contextual user profiles in a real world application.