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Statistics in Transition New Series

Polish Statistical Association

Central Statistical Office of Poland

Subject: Economics, Statistics & Probability


ISSN: 1234-7655
eISSN: 2450-0291





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VOLUME 19 , ISSUE 3 (September 2018) > List of articles


OlaOluwa S. Yaya

Keywords :  heteroscedasticity, inflation rate, structural breaks, unit root, OECD countries

Citation Information : Statistics in Transition New Series. Volume 19, Issue 3, Pages 477-493, DOI:

License : (BY-NC-ND 4.0)

Published Online: 13-December-2018



The need to understand the stationarity property of inflation of any country is paramount in the design of monetary targeting policy. In this paper, unit root hypotheses of inflation rates in 21 OECD countries are investigated using the newly proposed GARCH-based unit root tests with structural break and trend specifications. The results show that classical tests over-accept unit roots in inflation rates, whereas these tests are not robust to heteroscedasticity. As it is observed from the pre-tests, those tests with structural break reject more null hypotheses of unit roots of most inflation series than those without structural breaks. By applying variants of GARCH-based unit root tests, which include those with structural breaks and time trend regression specifications, we find that unit root tests without time trend give most rejections of the conventional unit roots. Thus, care should be taken while applying variants of the new unit root tests on weak trending time series as indicated in this work. Batteries of unit root tests for discriminating between stationarity and nonstationarity of inflation rates are recommended, since in the case of over-differenced series, wrong policy decision will be made, particularly when inflation series is considered in a cointegrating relationship with other variables. 

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