Browsing by Author "Ozdemir, Zeynel Abidin"

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Citation - WoS: 24
Citation - Scopus: 28
Are There Really Bubbles in Oil Prices?
(Elsevier Science Bv, 2014) Balcilar, Mehmet; Ozdemir, Zeynel Abidin; Yetkiner, Hakan
The aim of this paper is to identify bubbles in oil prices by using the exponential fitting methodology proposed by Watanabe et al. (2007) [28,29]. We use the daily US dollar closing crude oil prices of West Texas Intermediate (WTI) covering the 1986:01:02-2013:07:09 and the Brent for the 1987:05:20-2013:07:09 periods. The distinguishing feature of this study from the previous studies is that this is the first study in the literature showing the existence of bubbles in crude oil prices. We found that there are four distinct periods of persistent bubbles in the crude oil prices since 1986. Two of these persistent bubbles are before 2000 and two of them are after 2000. We conclude that further research is needed to understand better how futures markets may impact the oil price formation. (C) 2014 Elsevier B.V. All rights reserved.
Citation - WoS: 48
Citation - Scopus: 48
Lppls Bubble Indicators Over Two Centuries of the S&p 500 Index
(Elsevier, 2016) Zhang, Qunzhi; Sornette, Didier; Balcilar, Mehmet; Gupta, Rangan; Ozdemir, Zeynel Abidin; Yetkiner, Hakan
The aim of this paper is to present novel tests for the early causal diagnostic of positive and negative bubbles in the S&P 500 index and the detection of End-of-Bubble signals with their corresponding confidence levels. We use monthly S&P 500 data covering the period from August 1791 to August 2014. This study is the first work in the literature showing the possibility to develop reliable ex-ante diagnostics of the frequent regime shifts over two centuries of data. We show that the DS LPPLS (log-periodic power law singularity) approach successfully diagnoses positive and negative bubbles, constructs efficient End of-Bubble signals for all of the well-documented bubbles, and obtains for the first time new statistical evidence of bubbles for some other events. We also compare the DS LPPLS method to the exponential curve fitting and the generalized sup ADF test approaches and find that DS LPPLS system is more accurate in identifying well-known bubble events, with significantly smaller numbers of false negatives and false positives. (C) 2016 Elsevier B.V. All rights reserved.