One important difference between a recommender system and a traditional data mining system is that the end-user for the recommender system is the consumer. This difference leads to several desirable properties for recommender system algorithms that have not been explored in data mining algorithms.
Some recommendations are most valuable when they apply to a group of consumers rather than an individual. For instance, movies are most often attended socially. The choice of the right “date movie” can be very important. Recommenders can be used to select products that maximize the value of the product to a group of people. Some systems already support simple versions of this idea, such as selecting a movie that two people will like. Future multi-user recommendation systems will let customers control how the recommender system balances their interests in choosing a product. Should it choose a movie that neither will hate? That she will love? That they will both like? Different algorithms are needed for each of these scenarios to maximize the social good for the group, according to their needs.
The success of a recommender system should be measured by how effectively the system helps customers make decisions that they, retrospectively, consider correct. One interface innovation that can help customers decide when to follow recommendations is to explain the recommendation to the customer, just as many machine-learning algorithms explain their results to their users.
Researchers are currently experimenting with several different explanation models, including summarizing the data behind recommendations, explaining recommendations indirectly (e.g., indicating which of the customer's own preferences most strongly led to a particular recommendation), and providing "persuasive" evidence about the system's success in similar recommendations. Simpler explanation systems display a brief capsule of the amount of data or expected variance in a prediction. Additional research is needed regarding explanation algorithms for other recommender algorithms, and on the effectiveness of explanations in helping
customers decide among recommendations and increasing customer confidence in using recommender systems.