Recommender Systems

About 75% of what Netflix members watched came from some kind of recommendation, the company's engineers wrote in April 2012, in a post titled "Netflix Recommendations: Beyond the 5 stars". In October 2006 it had framed recommendation as predicting those stars, and offered a million dollars for predictions of held-out ratings 10% more accurate than its own system's; Chapter 5 told how the prize was won in 2009 by an ensemble Netflix never shipped. In between, the product changed. A DVD arrived by post and was rated afterwards, if at all. A streamed title is played, abandoned or finished, and every play is evidence that nobody had to type in.