Between two extremes: examining decompositions of the ensemble objective function

  • Authors:
  • Gavin Brown;Jeremy Wyatt;Ping Sun

  • Affiliations:
  • School of Computer Science, University of Manchester, Manchester;School of Computer Science, University of Birmingham, Birmingham;School of Computer Science, University of Birmingham, Birmingham

  • Venue:
  • MCS'05 Proceedings of the 6th international conference on Multiple Classifier Systems
  • Year:
  • 2005

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Abstract

We study how the error of an ensemble regression estimator can be decomposed into two components: one accounting for the individual errors and the other accounting for the correlations within the ensemble. This is the well known Ambiguity decomposition; we show an alternative way to decompose the error, and show how both decompositions have been exploited in a learning scheme. Using a scaling parameter in the decomposition we can blend the gradient (and therefore the learning process) smoothly between two extremes, from concentrating on individual accuracies and ignoring diversity, up to a full non-linear optimization of all parameters, treating the ensemble as a single learning unit. We demonstrate how this also applies to ensembles using a soft combination of posterior probability estimates, so can be utilised for classifier ensembles.