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Random walk and breaking trend in financial series: An econometric critique of unit root tests

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  • Rahman, Abdul
  • Saadi, Samir

Abstract

The present note sheds light on several pitfalls associated with unit root tests that are overlooked by a growing volume of literature in financial economics. Specifically, several studies have confused unit root tests with the Random Walk hypothesis. Unit root tests are not designed for such a task since they aim at investigating whether a time series is difference-stationary or trend-stationary and are not, therefore, predictability tests. Secondly, we emphasize some serious shortcomings associated with the widely used unit root test developed by Zivot and Andrews [Zivot, E. & Andrews, D.W.K. (1992). Further evidence on the great crash, the oil-price shock, and the unit-root hypothesis. Journal of Business and Economic Statistics, 10, 251-270.]. In particular, we stress that results from the Zivot-Andrews test are sensitive to the methods employed to calculate the critical values and to select the maxim lag k. Furthermore, Zivot-Andrews test imposes a one time structural break in a time series; however recent studies showed that not counting for other true structural breaks may bias the results and may cause a spurious rejection of the unit root null hypothesis. Finally, we support our arguments by an empirical example based on the findings of Narayan and Smyth [Narayan, K.P. & Smyth, R. (2004). Is South Korea's stock market efficient? Applied Economics Letters, 11, 707-710.] with regards to the efficiency of South Korean stock market. We show that contrary to what the authors claim, the KSE (KOSPI) price index is predictable, and hence the South Korean stock market is not informationally efficient.

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Bibliographic Info

Article provided by Elsevier in its journal Review of Financial Economics.

Volume (Year): 17 (2008)
Issue (Month): 3 (August)
Pages: 204-212

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Handle: RePEc:eee:revfin:v:17:y:2008:i:3:p:204-212

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Web page: http://www.elsevier.com/locate/inca/620170

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References

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  1. Chris Murray & Charles Nelson, 1998. "The Uncertain Trend in U.S. GDP," Discussion Papers in Economics at the University of Washington 0074, Department of Economics at the University of Washington.
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  16. Opong, Kwaku K. & Mulholland, Gwyneth & Fox, Alan F. & Farahmand, Kambiz, 1999. "The behaviour of some UK equity indices: An application of Hurst and BDS tests1," Journal of Empirical Finance, Elsevier, vol. 6(3), pages 267-282, September.
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  19. Samir Saadi & Devinder Gandhi & Shantanu Dutta, 2006. "Testing For Nonlinearity & Modeling Volatility In Emerging Capital Markets: The Case Of Tunisia," International Journal of Theoretical and Applied Finance (IJTAF), World Scientific Publishing Co. Pte. Ltd., vol. 9(07), pages 1021-1050.
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Cited by:
  1. Antonio E. Noriega & Daniel Ventosa-Santaulària, 2010. "Spurious Long-Horizon Regression in Econometrics," Working Papers 2010-06, Banco de México.
  2. Shyh-wei Chen, 2009. "Random walks in asian foreign exchange markets:evidence from new multiple variance ratio tests," Economics Bulletin, AccessEcon, vol. 29(2), pages 1296-1307.
  3. Suresh K. G. & Aviral Kumar Tiwari & Anto Joseph, 2012. "Are the emerging bric stock markets efficient?," Economics Bulletin, AccessEcon, vol. 32(2), pages 1261-1271.
  4. Chen, Shyh-Wei & Lin, Shih-Mo, 2014. "Non-linear dynamics in international resource markets: Evidence from regime switching approach," Research in International Business and Finance, Elsevier, vol. 30(C), pages 233-247.
  5. Abullah M. Noman & Minhaz U. Ahmed, 2008. "Efficiency of the foreign exchange markets in South Asian Countries," AIUB Bus Econ Working Paper Series AIUB-BUS-ECON-2008-18, American International University-Bangladesh, Office of Research and Publications (ORP), revised Jun 2008.

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