
Marina Meila
University of Washington, USA
Friday 14 November 2008
15.30
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Consensus finding, exponential models, and infinite rankings
This talk is concerned with summarizing  by means of statistical models  of data that expresses preferences. This data is typically a set of rankings of n items by a panel of experts; the simplest summary is the "consensus ranking", or the "centroid" of the set of rankings. Such problems appear in many tasks, ranging from combining voter preferences to boosting of search engines.
We study the problem in its more general form of estimating a parametric model known as the Generalized Mallows (GM) model. I will present an exact estimation algorithm, nonpolynomial in theory, but extremely effective in comparison with existing algorithms. From a statistical point of view, we show that the GM model is an exponential family, and introduce the conjugate prior for this model class.
Then we introduce the infinite GM model, corresponding to "rankings" over an infinite set of items, and show that this model is both elegant and of practical significance. Finally, the talk will touch upon the subject of multimodal distributions and clustering.
Joint work with: Bhushan Mandhani, Le Bao, Kapil Phadnis, Arthur Patterson and Jeff Bilmes