A recursive prediction algorithm for collaborative filtering recommender systems

Collaborative filtering (CF) is a successful approach for building online recommender systems. The fundamental process of the CF approach is to predict how a user would like to rate a given item based on the ratings of some nearest-neighbor users (user-based CF) or nearest-neighbor items (item-based CF). In the user-based CF approach, for example, the conventional prediction procedure is to find some nearest-neighbor users of the active user who have rated the given item, and then aggregate their rating information to predict the rating for the given item. In reality, due to the data sparseness, we have observed that a large proportion of users are filtered out because they don't rate the given item, even though they are very close to the active user. In this paper we present a recursive prediction algorithm, which allows those nearest-neighbor users to join the prediction process even if they have not rated the given item. In our approach, if a required rating value is not provided explicitly by the user, we predict it recursively and then integrate it into the prediction process. We study various strategies of selecting nearest-neighbor users for this recursive process. Our experiments show that the recursive prediction algorithm is a promising technique for improving the prediction accuracy for collaborative filtering recommender systems.