NetflixNetflix is a subscription-based movie and

television show rental service that offers media to subscribers: Physically by mail Over the internet

Has a catalog of over 100,000 movies and television shows

Subscriber base of over 10 million

RecommendationsNetflix offers users the ability to rate movies

and television shows that they have seenDepending on those ratings, Netflix provides

recommendations of movies and television shows that the subscriber would like to watch

These recommendations are based on an algorithm called Cinematch

CinematchUses straightforward statistical linear models

with a lot of data conditioningThis means that the more a subscriber rates,

the more accurate the recommendations will become

Netflix PrizeCompetition for the best collaborative filtering

algorithm to predict user ratings for movies and television shows, based on previous ratings

Offered a $1 million prize to the team who could improve Cinematch’s accuracy by 10%

Awarded a $50,000 progress prize for the team who makes the most progress for each year before the 10% mark was reached

The contest started on October 2, 2006 and would run until at least October 2, 2011, depending on when a winner was chosen

MetricsThe accuracy of the algorithms was

measured by using root mean square error, or RMSE

Chosen because it is a well-known, single value that can account for and amplify the contributions of errors such as false positives and false negatives

MetricsCinematch scored 0.9525 on the test subsetThe winning team needed to score at least

10% lower, with an RMSE of 0.8563

ResultsThe contest ended on June 26, 2009The threshold was broken by the teams

“BellKor's Pragmatic Chaos” and “The Ensemble”, both achieving a 10.06% improvement over Cinematch, with an RMSE of 0.8567

“BellKor's Pragmatic Chaos” won the prize due to the team submitting their results 20 minutes before “The Ensemble”

Netflix Prize SequelDue to the success of their contest, Netflix

announced another contest to further improve their recommender system

Unfortunately, it was discovered that the anonymized customer data that they provided to the contestants could actually be used to identify individual customers

This, combined with a resulting investigation by the FTC and a lawsuit, led Netflix to cancel their sequel

Sourceshttp://blog.netflix.com/2010/03/this-is-neil-hunt-chief-

product-officer.htmlhttp://www.netflixprize.comhttp://www.nytimes.com/2010/03/13/technology/

13netflix.html?_r=1