The EnsembleGrand Prize Team, captained by Gábor Takács of Gravity R&D, has been one of the leading teams in the Netflix Prize competition throughout 2009. At one point this spring, the slimmest of possible margins (0.01%) separated Grand Prize Team in third place from the two teams tied for the lead. Leading shareholders in Grand Prize Team (a.k.a. GPT) include Joe Sill, Ces Bertino and the members of the two teams who founded GPT, Gravity and Dinosaur Planet.
GPT was founded on the notion that collaboration was the key to victory in the Netflix Prize competition. Gravity and Dinosaur Planet had already shown what collaboration could accomplish. They had previously joined forces to form the team When Gravity and Dinosaurs Unite, rising to first place on the leaderboard on the day before the deadline for submissions for the first Progress Prize of the competition in October 2007. They were edged out by the AT&T team KorBell in the final hours, but the power of partnerships had been demonstrated in dramatic fashion.
Gravity is a team of four researchers from Hungary: Gábor Takács (Szechenyi Istvan University, Gyor) and István Pilászy, Bottyán Németh, and Domonkos Tikk (Budapest University of Technology and Economics). They form not only a Netflix Prize team but also the core of a company, Gravity R & D. Gravity held the top spot on the leaderboard for several months during the first year of the competition. Dinosaur Planet, another leading Netflix Prize team during the first year, was formed by three students from the Princeton class of 2007: Lester Mackey, David Weiss, and David Lin. Mackey and Weiss have since moved on to computer science PhD programs at UC Berkeley and University of Pennsylvania, respectively, while Lin works in finance in New York.
Gravity and Dinosaur Planet decided in January 2009 to take the concept of collaboration to a new level by creating a team which issued a standing invitation to any other Netflix Prize competitor to submit techniques and results to be assessed for the potential to boost the score of the combined team. The deal offered to the rest of the competitors seemed eminently fair. At the time of formation, the union of the two founding teams had already achieved 9% of the 10% improvement required to win the Netflix Prize, but that final 1% was such a daunting challenge that the founders were willing to offer a two-thirds share of the prize ($666,666 USD) to additional collaborators. Shares would be granted in proportion to the size of the contribution each collaborator made towards that elusive 1%. Thus, an improvement in the leaderboard score of 0.0001, or just one basis point (0.01%), was likely to be worth nearly seven thousand dollars. Gábor Takács was chosen to captain the new team, which was named Grand Prize Team out of a spirit of optimism.
Bottyán Németh of Gravity designed a server which could quickly yet rigorously analyze files produced by models from GPT applicants, searching for indications that the applicant's submission could improve the team's score by providing something complementary to the models the team had already developed. Anyone could upload submissions at any time of day or night and get a quick response from the server indicating whether the submission was promising. Applicants were also invited to send modeling software to GPT for evaluation for possible synergies. Submitting a result which could help GPT was a difficult task, given the high position on the leaderboard which the team already held. Many applicants were unable to demonstrate any ability to improve upon the set of models GPT had already developed.
Nonetheless, the "open invitation" strategy quickly paid off when Ces Bertino, a software engineer working in San Diego, submitted results to GPT. Bertino already had one of the best single-person teams in the entire competition and had held a top 10 position on the leaderboard for many months. Bertino's submissions provided an improvement of 21 basis points (0.21%) - an enormous jump in a competition where leading teams would rejoice when making improvements of just a few basis points.
Grand Prize Team then collected additional important contributions from Netflix Prize competitors from around the world, such as Wojtek Kulik, Bill Roberts and Willem Mestrom. Kulik is a predictive modeling researcher and entrepreneur in Warsaw, Poland. Roberts is a researcher in statistical signal processing and a part-time faculty member at George Washington University in Washington DC. Mestrom is a computational scientist and software engineer in the Netherlands.
Joe Sill, a machine learning PhD from Caltech with dotcom and finance experience, submitted technology in February which proved highly promising when evaluated by Takács. After refining the software Sill submitted, Takács found that it could boost GPT's score by 14 basis points, another major jump. Then Dan Nabutovsky, an algorithm designer from Israel, contributed a substantial improvement of 6 basis points, and the possibility that GPT might challenge for the top spot on the leaderboard began to look more likely. Sill continued to submit enhancements and accrued 8 more basis points of improvement, eked out a few basis points at a time. As a result, GPT rose to within just one basis point of the top position on the leaderboard in May, achieving a score of 0.8597 while Pragmatic Theory and BellKor in Big Chaos (two teams who would later merge to form BellKor's Pragmatic Chaos) were tied in first, each with a score of 0.8596. When BellKor's Pragmatic Chaos broke the million dollar barrier in late June, Grand Prize Team had a score of 0.8594, the best score of any team not participating in the BellKor's Pragmatic Chaos coalition.
After the breaking of the million dollar barrier, only 30 days remained for other teams to attempt to catch BellKor's Pragmatic Chaos. For the final push, GPT brought on board David Purdy, who is finishing a statistics PhD at UC Berkeley. Purdy contributed a number of analyses which had not yet been pursued by other GPT members and a wide-ranging perspective on the statistics literature.
In the closing days of the competition, GPT decided that it wasn't finished pursuing a cooperative approach to the Netflix Prize. Talks with another leading team, Opera Solutions and Vandelay United, led to the formation of The Ensemble.
