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Improving Predictions using Ensemble Bayesian Model Averaging

Published online by Cambridge University Press:  04 January 2017

Jacob M. Montgomery ,
Florian M. Hollenbach  and
Michael D. Ward
Jacob M. Montgomery
Affiliation:
Department of Political Science, Washington University in St Louis, Campus Box 1063, One Brookings Drive, St Louis, MO 63130-4899
Florian M. Hollenbach
Affiliation:
Department of Political Science, Duke University, Perkins Hall 326, Box 90204, Durham, NC 27707-4330
Michael D. Ward*
Affiliation:
Department of Political Science, Duke University, Perkins Hall 326, Box 90204, Durham, NC 27707-4330
*
e-mail: michael.d.ward@duke.edu (corresponding author)
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Abstract

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We present ensemble Bayesian model averaging (EBMA) and illustrate its ability to aid scholars in the social sciences to make more accurate forecasts of future events. In essence, EBMA improves prediction by pooling information from multiple forecast models to generate ensemble predictions similar to a weighted average of component forecasts. The weight assigned to each forecast is calibrated via its performance in some validation period. The aim is not to choose some “best” model, but rather to incorporate the insights and knowledge implicit in various forecasting efforts via statistical postprocessing. After presenting the method, we show that EBMA increases the accuracy of out-of-sample forecasts relative to component models in three applied examples: predicting the occurrence of insurgencies around the Pacific Rim, forecasting vote shares in U.S. presidential elections, and predicting the votes of U.S. Supreme Court Justices.

Type
Research Article
Information
Political Analysis , Volume 20 , Issue 3 , Summer 2012 , pp. 271 - 291
Copyright
Copyright © The Author 2012. Published by Oxford University Press on behalf of the Society for Political Methodology 

Footnotes

Authors' note: For generously sharing their data and models with us, we thank Alan Abramowitz, James Campbell, Robert Erikson, Ray Fair, Douglas Hibbs, Michael Lewis-Beck, Andrew D. Martin, Kevin Quinn, Stephen Shellman, Charles Tien, and Christopher Wlezien. We especially want to thank Adrian Raftery and Brendan Nyhan for their encouragement and feedback as this project evolved. The editor and the reviewers of Political Analysis provided especially salient suggestions that substantially improved our research.

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