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Thesis Defense - Bonnlander

Nonparametric Selection of Input Variables for Connectionist Learning
Computer Science PhD Candidate

When many possible input variables to a statistical model exist, removing unimportant inputs can improve the model's performance significantly. A new method for selecting input variables is proposed. Components for the proposed method include:

Analysis of mutual information shows that it is natural measure of input variable relevance. It is a more general measure of input variable relevance than expected conditional variance. Under certain conditions, the two measures order the relevance of input variable subsets in precisely the same manner, but these conditions do not generally hold. An unbiased approximation to mutual information exists, but it is unbiased only if the underlying probabilities are exact.

Analysis of kernel density estimation shows that the accuracy of mutual information estimates depends directly on how densely populated the points in the data set are. However, for a range of explored problems, the relative ordering of mutual information estimates remains correct, despite inaccuracies in individual estimates.

Analysis of forward selection explores the amount of data required to select a certain number of relevant input variables. It is shown that in order to select a certain number of relevant input variables, the amount of required data increases roughly exponentially as more relevant input variables are considered. It is also shown that the chances of forward selection ending up in a local minimum are reduced by bootstrapping the data.

Finally, the method is compared to two connectionist methods for input variable selection: Sensitivity Based Pruning and Automatic Relevance Determination. It is shown that the new method outperforms these two when the number of independent, candidate input variables is large. However, the method requires the number of relevant input variables to be relatively small. These results are confirmed on a number of real world prediction problems, including the prediction of energy consumption in a building, the prediction of heart rate in a patient with sleep apnea, and the prediction of wind force in a wind turbine.

Committee: Andreas Weigend, Assistant Professor (Chair)
Michael Mozer, Associate Professor
Clayton Lewis, Professor
Kelvin Wagner, Department of Electrical and Computer Engineering
Richard Holley, Department of Mathematics
Department of Computer Science
University of Colorado Boulder
Boulder, CO 80309-0430 USA
May 5, 2012 (14:20)