Session: Algorithms 1
Chair: Robin Burke
Date: Friday, October 23, 10:30-12:10
- A spatio-temporal approach to collaborative filtering
by Zhengdong Lu, Deepak Agarwal, Inderjit S. Dhillon
In this paper, we propose a novel spatio-temporal model for collaborative filtering applications. Our model is based on low-rank matrix factorization that uses a spatio-temporal filtering approach to estimate user and item factors. The spatial component regularizes the factors by exploiting correlation across users and/or items, modeled as a function of some implicit feedback (e.g., who rated what) and/or some side information (e.g., user demographics, browsing history). In particular, we incorporate correlation in factors through a Markov random field prior in a probabilistic framework, whereby the neighborhood weights are functions of user and item covariates. The temporal component ensures that the user/item factors adapt to process changes that occur through time and is implemented in a state space framework with fast estimation through Kalman filtering. Our spatio-temporal filtering (ST-KF hereafter) approach provides a single joint model to simultaneously incorporate both spatial and temporal structure in ratings and therefore provides an accurate method to predict future ratings. To ensure scalability of ST-KF, we employ a mean-field approximation for inference. Incorporating user/item covariates in estimating neighborhood weights also helps in dealing with both cold-start and warm-start problems seamlessly in a single unified modeling framework; covariates predict factors for new users and items through the neighborhood. We illustrate our method on simulated data, benchmark data and data obtained from a relatively new recommender system application arising in the context of Yahoo! Front Page.
- Pairwise preference regression for cold-start recommendation
by Seung-Taek Park, Wei Chu
Recommender systems are widely used in online e-commerce applications to improve user engagement and then to increase revenue. A key challenge for recommender systems is providing high quality recommendation to users in “cold-start” situations. We consider three types of cold-start problems: 1) recommendation on existing items for new users; 2) recommendation on new items for existing users; 3) recommendation on new items for new users. We propose predictive feature-based regression models that leverage all available information of users and items, such as user demographic information and item content features, to tackle cold-start problems. The resulting algorithms scale efficiently as a linear function of the number of observations. We verify the usefulness of our approach in three cold-start settings on the MovieLens and EachMovie datasets, by comparing with five alternatives including random, most popular, segmented most popular, and two variations of Vibes affinity algorithm widely used at Yahoo! for recommendation.
- Ordering innovators and laggards for product categorization and recommendation
by Sarah K. Tyler, Shenghuo Zhu, Yun Chi, Yi Zhang
Different buyers exhibit different purchasing behaviors. Some rush to purchase new products while others tend to be more cautious, waiting for reviews from people they trust. In market analysis, the former group of buyers is often referred to as innovators and early adopters while the latter group is referred to as laggards. The adoption behavior is a dynamic feature of the user and varies over groups of products, e.g., innovators of literature may not be the innovators of electronics. The adoption order of users is a dynamic feature of the product, which can help to predict the future potential buyers. However, such dynamic features are usually unavailable in the description of products. In this paper, we study the user behavior of an online review website- Epinions.com. We first propose to model user adoption behaviors by creating a total ordering among users who rate the products in a given category. We develop a greedy algorithm and a Markov-chain based algorithm for computing the category total ordering. Next, we show that by using user behavior information, we can more accurately predict the category of a new product as well as predict which users will follow. Furthermore, by using the Epinion.com trust network as evidence, we demonstrate that our total ordering can group users into communities that closely resemble the trust network. Thus the adoption order can be a useful feature in recommendation systems.
- Improving rating estimation in recommender systems using aggregation- and variance-based hierarchical models
by Akhmed Umyarov, Alexander Tuzhilin
Previous work on using external aggregate rating information showed that this information can be incorporated in several different types of recommender systems and improves their performance. In this paper, we propose a more general class of methods that combine external aggregate information with individual ratings in a novel way. Unlike the previously proposed methods, one of the defining features of this approach is that it takes into the consideration not only the aggregate average ratings but also the variance of the aggregate distribution of ratings. The methods proposed in this paper estimate unknown ratings by finding an optimal linear combination of individual-level and aggregate-level rating estimators in a form of a hierarchical regression (HR) model that is grounded in the theory of statistics and machine learning.
The proposed HR model is general enough so that the standard individual-level recommender systems and naive aggregate methods constitute special cases of this model.
We show that for the general HR model, the presence of the aggregate variance, surprisingly, does not significantly improve estimation of unknown ratings vis-a-vis the case when only aggregate average ratings are considered.
In the paper, we experimentally show that the optimal linear combination approach significantly dominates all other special cases, including the classical non-aggregated case and our previously studied aggregate methods, and therefore is the method of choice.
RecSys 2009 (New York)
Sponsors and Benefactors
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |