The weekly SILO Seminar Series is made possible through the generous support of the 3M Company and its Advanced Technology Group


with additional support from the Analytics Group of the Northwestern Mutual Life Insurance Company

Northwestern Mutual

Unsupervised Ranking and Ensemble Learning

Boaz Nadler, Prof.

Date and Time: May 07, 2014 (12:30 PM)
Location: Orchard room (3280) at the Wisconsin Institute for Discovery Building


In various decision making problems, one is given the advice or predictions of several classifiers of unknown reliability,over multiple questions or queries. This scenario is different from the standard supervised setting where classifier accuracy can be assessed usingavailable labeled training or validation data, and raises several questions: given only the predictions of several classifiers of unknown accuracies, over a large set of unlabeled test data, is it possible to a) reliably rank them, and b) construct a meta-classifier more accurate than anyindividual classifier in the ensemble?

In this talk we'll show that under standard independence assumptions between classifier errors, this high dimensional data hides a simple low dimensional structure. In particular, we'll present a novel spectral approach to address the above questions, and derive a novel unsupervised spectral meta-learner (SML). On both simulated and real data, SML typically achieves a higher accuracy than most classifiers in the ensemble and can provide a better startingpoint for iterative estimation of the maximum likelihood estimator than classical majority voting. Furthermore, SML is robust to the presence of small malicious groups of classifiers designed to veer the ensemble prediction away from the (unknown) ground truth.

Joint work with Fabio Parisi, Francesco Strino and Yuval Kluger (Yale).