Back in July, I posted here about the $1 million Netflix Prize and the amazing accomplishment of one of our senior research scientists, Yehuda Koren. At the time, Yehuda and a team of academic and industry researchers from around the world had cracked the mythical 10-percent threshold in the contest – making their team, BellKor’s Pragmatic Chaos, contenders for the grand prize. In a dramatic turn of events at the finish line, the team ended up tied with another group of researchers that submitted a similar improvement later that same day.

But today, at a press conference in New York, after verifying the results with their top technical brass, Netflix officially declared Yehuda and his team the grand prize champions. To achieve this honor, they bested 41,305 teams from 186 countries.

To reiterate, this was no easy feat. Every person in the world has a different taste in movies. Yehuda, for example, loves the Godfather, but is not much of a James Bond fan (whether it’s Connery, Moore, Daulton, Brosnan, Craig, or the other guy). And it’s not just Yehuda -- everyone has personal tastes that don’t perfectly correspond to box office results, DVD sales, or Academy Awards. As a result, figuring out what movies should be recommended to you is an intense scientific problem.

In fact, it is such an impressive piece of research that Yehuda’s paper detailing one of his main contributions to the prize-winning team won the best paper award at KDD-09 (otherwise know as 15th ACM SIGKDD Conference on Knowledge Discovery and Data Mining).

It’s too complicated a paper to summarize here with any justice, but let me give you the gist: Yehuda figured out that the way people rate movies on Netflix changes over time and, in some cases, from day to day. In other words, not only do my tastes “mature” and shift, but so do my moods. For example, on a Monday, perhaps out of frustration with having to be back in the office, maybe I’m a little harsh on the movie I watched Sunday night, which I give a 1-star rating in spite of it not being that terrible. On the other hand, that film I saw with my kids when we were on vacation – the one that had them laughing all night -- gets a warm-hearted 5 stars when it wasn’t exactly an aesthetic masterpiece. Yehuda laid down the research to mathematically model this phenomenon and it’s a major reason why his team cracked the code to get over 10-percent.

Ultimately, this exactly why we founded Yahoo! Labs -- to encourage Yahoos to think outside of our own sandbox and contribute to industry-wide technical and scientific challenges that will some day make your online life easier. Sometimes that means just making sure there’s less spam in your email inbox and -- in this case -- making sure that your Netflix queue is filled with movies you’re really going to like.

• New York Times - Netflix Awards $1 Million Prize and Starts a New Contest
• Forbes - The Netflix R&D Game
• Fortune - Box office boffo for brainiacs: The Netflix Prize

Prabhakar Raghavan
Head of Yahoo! Labs