本篇論文主要是依據Patton(2006)與Huang et al.(2009)的研究,將copula-GARCH方法應用至美國的不動產投資信託市場中,以探討模型是否能有效改善對於REITs資產組合風險值的預測能力及績效。我們使用美國國家不動產投資信託協會之REITs指數(FTSE NAREIT US Real Estate Index - All REITs)與S&P 500股價指數組成投資組合,並使用GARCH模型來描述指數報酬率序列相關的特性,最後以5個常數copula與2類動態copula共7種copula函數分別搭配個別資產報酬率服從常態分配與Student-t分配之GARCH(1,1)模型共組合出14種copula-GARCH模型來估計兩資產報酬率的聯合分配,進而推導出投資組合的一日風險值,樣本期間涵蓋金融風暴發生前後共2800個觀察值,並與一般風險值估計方法進行回溯測試結果的比較。Copula-GARCH模型同時考慮了個別指數報酬率序列相關的性質與不同金融資產間非線性相關的部分,並且修正了傳統風險值模型之常態性假設所無法捕捉到的資產分配現象,本研究的實證結果顯示,邊際分配服從GARCH-t之time-varying SJC copula不論在市場狀況好壞時相對於傳統風險值模型確實能夠更加精確的掌握REITs資產組合的風險。
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