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NEGATIVE VOLATILITY SPILLOVERS IN THEUNRESTRICTED ECCC-GARCH MODEL

Published online by Cambridge University Press:  26 October 2009

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Abstract

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This paper considers a formulation of the extendedconstant or time-varying conditional correlationGARCH model that allows for volatility feedback ofeither the positive or negative sign. In theprevious literature, negative volatility spilloverswere ruled out by the assumption that all theparameters of the model are nonnegative, which is asufficient condition for ensuring the positivedefiniteness of the conditional covariance matrix.In order to allow for negative feedback, we showthat the positive definiteness of the conditionalcovariance matrix can be guaranteed even if some ofthe parameters are negative. Thus, we extend theresults of Nelson and Cao (1992) and Tsai and Chan(2008) to a multivariate setting. For the bivariatecase of order one, we look into the consequences ofadopting these less severe restrictions and findthat the flexibility of the process is substantiallyincreased. Our results are helpful for themodel-builder, who can consider the unrestrictedformulation as a tool for testing various economictheories.

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Type
Research Article
Copyright
Copyright © Cambridge University Press 2009