Remembering the stars?: effect of time on preference retrieval from memory.

ABSTRACTMany recommendation systems rely on explicit ratings provided by their users. Often these ratings are provided long after consuming the item, relying heavily on people's representation of the quality of the item in memory. This paper investigates a psychological process, the "positivity effect", that influences the retrieval of quality judgments from our memory by which pleasant items are being processed and recalled from memory more effectively than unpleasant items. In an offline study on the MovieLens data we used the time between release date and rating date as a proxy for the time between consumption and rating. Ratings for movies tend to increase over time, consistent with the positivity effect. A subsequent online user study used a direct measure of time between rating and consumption, by asking users to rate movies (recently aired on television) and to explicitly report how long ago they watched these movies. In contrast to the offline study we find that ratings tend to decline over time showing reduced accuracy in ratings for items experienced long ago. We discuss the impact these rating dynamics might have on recommender algorithms, especially in cases where a new user has to submit his preferences to a system.