VOLATİLİTEDE UZUN HAFIZA VE YAPISAL KIRILMA: BORSA İSTANBUL ÖRNEĞİ*

Bu çalışmanın amacı Borsa İstanbul’da etkin piyasalar hipotezinin geçerliliğini ampirik olarak araştırmaktır. Bu amaçla 1988 ile 2014 yılları arasında BİST100 ve BİST30 endeksleri için günlük kapanış verileri kullanılarak getiri serileri oluşturulmuş ve getiri serilerinin koşullu varyansında uzun hafızanın varlığı Baillie ve Morana (2009) tarafından geliştirilen Uyarlanabilir (Adaptive)-FIGARCH (A-FIGARCH) model ile araştırılmıştır. Analiz sonucunda, endeks getirilerinin varyansında çok sayıda yapısal kırılma noktası bulunmuş ve A-FIGARCH modelin getiri serilerini tahmin etmede daha üstün sonuçlar verdiği belirlenmiştir. Ayrıca, getiri serilerinin koşullu varyansının uzun hafıza özelliği gösterdiği ve buna bağlı olarak Borsa İstanbul’un zayıf formda etkin olmadığı sonucuna ulaşılmıştır.

Anahtar Kelimeler:

Etkin Piyasa Hipotezi, Uzun Hafıza, Rassal Yürüyüş, A-FIGARCH

LONG MEMORY AND STRUCTURAL BREAKS ON VOLATILITY: EVIDENCE FROM BORSA ISTANBUL

The aim of this paper is to examine validity of the efficient market hypothesis in Borsa İstanbul. Daily returns series are calculated by using daily closing price for BİST100 and BİST30 indices for periods of 1988-2014 and the presence of long memory on the volatility of the returns series is examined by means of Adaptive-FIGARCH (A-FIGARCH) model proposed by Baillie and Morana (2009). Empirical results suggest that there are multiple structural breaks on variance of returns series and A-FIGARCH model outperforms. In addition, it is found evidence in favor of long memory on the conditional variance of returns series and hence it can be said that Borsa İstanbul is not weak form efficient market.

Keywords:

Efficient Market Hypothesis, Long Memory, Random Walk, A-FIGARCH,

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