Amazon, for example, avoided this start-up problem by collecting preferences that were implicit in people’s actions. Customers who ordered books or music from Amazon implicitly expressed their preference for the titles they bought over the titles they did not buy. Customers who bought the same book or CD were likely to have similar preferences for other titles as well. Similarly, collaborative filtering could use customers’ behavior while surfing a site to infer their tastes. Search behavior, the amount of time a customer spent on a given product, and similar metrics could be used to indirectly infer a preference without requiring tedious data entry on the customer’s part