SMS scnews item created by Uri Keich at Fri 10 Sep 2010 1701
Type: Seminar
Distribution: World
Expiry: 17 Sep 2010
Calendar1: 17 Sep 2010 1400-1500
CalLoc1: Carslaw 173
Auth: uri@purix (assumed)

# Statistics Seminar: John Ormerod -- Skew-Normal Variational Approximations

John Ormerod School of Mathematics and Statistics University of Sydney

Location: Carslaw 173

Time: 2pm Friday, September 17, 2010

Title: Skew-Normal Variational Approximations

Abstract: High-dimensional analytically intractable integrals are a pervasive problem in
Bayesian inference.  Monte Carlo methods can be used in the analysis of models where
such problems arise.  However, for large datasets or complex models such methods become
computationally burdensome and it may become desirable to seek alternatives.

Popular deterministic alternatives include variational Bayes and Laplace’s method.
However, variational Bayes only performs well under particular conjugacy and
independence assumptions and Laplace’s method only works well when the posterior is
nearly normal in shape.

In this talk I introduce the skew-normal variational approximation which minimises the
Kullback-Leibler distance between a posterior density and a multivariate skew-normal
density.  The resulting approximation often simplifies calculations to the maximisation
of a sum of univariate integrals which may be handled using a combination of standard
optimisation and quadrature techniques.  It is shown for a number of examples that the
approach is more accurate than variational Bayes and Laplace’s method whilst remaining
faster than standard Monte Carlo methods.


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