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On PPP, unit roots and panels


  • Martin Wagner



This paper re-assesses the panel (unit root test) evidence for PPP on four monthly data sets. We discuss and illustrate that commonly-used first generation panel unit root tests are inappropriate for PPP analysis since they are constructed for cross-sectionally uncorrelated panels. Given that real exchange rate panel data sets are – almost by construction – highly cross-sectionally correlated, so called second generation panel unit root methods that allow for and model cross-sectional dependence should be applied. Using inappropriate first generation tests, quite strong evidence for PPP is found. However, this evidence vanishes entirely when resorting to an appropriate method (e.g. the one developed in Bai and Ng, 2004a) for nonstationary cross-sectionally correlated panels. We strongly believe that our findings are relevant beyond the data sets investigated here for illustration.
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Suggested Citation

  • Martin Wagner, 2008. "On PPP, unit roots and panels," Empirical Economics, Springer, vol. 35(2), pages 229-249, September.
  • Handle: RePEc:spr:empeco:v:35:y:2008:i:2:p:229-249 DOI: 10.1007/s00181-007-0156-z

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    1. Raihan, Selim & Abdullah, S M & Barkat, Aroni & Siddiqua, Salina, 2017. "Mean Reversion of the Real Exchange Rate and the validity of PPP Hypothesis in the context of Bangladesh: A Holistic Approach," MPRA Paper 77172, University Library of Munich, Germany.
    2. Syed A. Basher & Josep Lluis Carrión-i-Silvestre, 2008. "Deconstructing Shocks and Persistence in OECD Real Exchange Rates," Working Papers XREAP2008-06, Xarxa de Referència en Economia Aplicada (XREAP), revised Jun 2008.
    3. Wagner, Martin, 2008. "The carbon Kuznets curve: A cloudy picture emitted by bad econometrics?," Resource and Energy Economics, Elsevier, vol. 30(3), pages 388-408, August.
    4. García Solanes, José & Torrejón-Flores, Fernando, 2009. "The Balassa-Samuelson Hypothesis in Developed Countries and Emerging Market Economies: Different Outcomes Explained," Economics - The Open-Access, Open-Assessment E-Journal, Kiel Institute for the World Economy (IfW), vol. 3, pages 1-24.
    5. Jorg Breitung & Gianluca Cubadda, 2009. "Testing for cointegration in high-dimensional systems," CEIS Research Paper 148, Tor Vergata University, CEIS, revised 30 Sep 2009.
    6. Herwartz, Helmut & Siedenburg, Florian, 2009. "A new approach to unit root testing," Economics Working Papers 2009-06, Christian-Albrechts-University of Kiel, Department of Economics.
    7. Syed, Munawar-Shah & Mariani, Abdul-Majid & Syed, Hussain-Shah, 2014. "Assessing Fiscal Sustainability for SAARC and IMT-GT Countries," MPRA Paper 62815, University Library of Munich, Germany, revised 2014.
    8. Smeekes Stephan, 2011. "Bootstrap Sequential Tests to Determine the Stationary Units in a Panel," Research Memorandum 003, Maastricht University, Maastricht Research School of Economics of Technology and Organization (METEOR).
    9. García-Solanes, José & Sancho-Portero, F. Israel & Torrejón-Flores, Fernando, 2008. "Beyond the Balassa-Samuelson effect in some new member states of the European Union," Economic Systems, Elsevier, vol. 32(1), pages 17-32, March.
    10. Wagner, Martin, 2005. "The Balassa-Samuelson Effect in 'East & West'. Differences and Similarities," Economics Series 180, Institute for Advanced Studies.
    11. Miguel Carvalho & Paulo Júlio, 2012. "Digging out the PPP hypothesis: an integrated empirical coverage," Empirical Economics, Springer, vol. 42(3), pages 713-744, June.
    12. Markus Eberhardt & Christian Helmers & Hubert Strauss, 2013. "Do Spillovers Matter When Estimating Private Returns to R&D?," The Review of Economics and Statistics, MIT Press, vol. 95(2), pages 436-448, May.
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    14. Helmut Herwartz & Florian Siedenburg, 2010. "A New Approach to Unit Root Testing," Computational Economics, Springer;Society for Computational Economics, vol. 36(4), pages 365-384, December.
    15. Castrén, Olli & Osbat, Chiara & Sydow, Matthias, 2006. "What drives investors' behaviour in different FX market segments? A VAR-based return decomposition analysis," Working Paper Series 706, European Central Bank.

    More about this item


    PPP; Real exchange rate index; Unit root; Panel; Cross-sectional dependence; Factor model; C23; F30; F31;

    JEL classification:

    • C23 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables - - - Models with Panel Data; Spatio-temporal Models
    • F30 - International Economics - - International Finance - - - General
    • F31 - International Economics - - International Finance - - - Foreign Exchange


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