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A NECESSARY MOMENT CONDITION FOR THEFRACTIONAL FUNCTIONAL CENTRAL LIMITTHEOREM

Published online by Cambridge University Press:  25 November 2011

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Abstract

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We discuss the moment condition for the fractionalfunctional central limit theorem (FCLT) for partialsums of xt =Δ−dut,where $d\, \in \,\left({ - {1 \over 2}\,,\,{1
                                                  \over 2}} \right)$ isthe fractional integration parameter andut is weaklydependent. The classical condition is existence ofq ≥ 2 and $q\, > \,\left( {d\, + \,{1 \over
                                                  2}} \right)^{ - 1} $moments of the innovation sequence. Whend is close to $ -
                                                  {1 \over 2}$ thismoment condition is very strong. Our main result isto show that when $d\, \in \,\left({ - \,{1 \over 2},\,0}
                                                  \right)$ and undersome relatively weak conditions onut, the existence of$q\, \ge \,\left({d\, + \,{1 \over 2}}
                                                  \right)^{ - 1} $moments is in fact necessary for the FCLT forfractionally integrated processes and that$q\, > \,\left( {d\, + \,{1 \over
                                                  2}} \right)^{ - 1} $moments are necessary for more general fractionalprocesses. Davidson and de Jong (2000,Econometric Theory 16, 643–666)presented a fractional FCLT where onlyq > 2 finite moments areassumed. As a corollary to our main theorem we showthat their moment condition is not sufficient andhence that their result is incorrect.

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Brief Report
Copyright
Copyright © Cambridge University Press 2011