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Commodity Prices And Unit Root Tests

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  • Wang, Dabin
  • Tomek, William G.

Abstract

Endogenous variables in structural models of agricultural commodity markets are typically treated as stationary. Yet, tests for unit roots have rather frequently implied that commodity prices are not stationary. This seeming inconsistency is investigated by focusing on alternative specifications of unit root tests. We apply various specifications to Illinois farm prices of corn, soybeans, barrows and gilts, and milk for the 1960 through 2002 time span. The preponderance of the evidence suggests that nominal prices do not have unit roots, but under certain specifications, the null hypothesis of a unit root cannot be rejected, particularly when the logarithms of prices are used. If the test specification does not account for a structural change that shifts the mean of the variable, the results are biased toward concluding that a unit root exists. In general, the evidence does not favor the existence of unit roots.

Suggested Citation

  • Wang, Dabin & Tomek, William G., 2004. "Commodity Prices And Unit Root Tests," 2004 Annual meeting, August 1-4, Denver, CO 20141, American Agricultural Economics Association (New Name 2008: Agricultural and Applied Economics Association).
    • Handle: RePEc:ags:aaea04:20141
    DOI: 10.22004/ag.econ.20141
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    as
    1. Chambers, Marcus J., 2004. "Testing for unit roots with flow data and varying sampling frequency," Journal of Econometrics, Elsevier, vol. 119(1), pages 1-18, March.
    2. Peter C.B. Phillips & Sam Ouliaris & Joon Y. Park, 1988. "Testing for a Unit Root in the Presence of a Maintained Trend," Cowles Foundation Discussion Papers 880, Cowles Foundation for Research in Economics, Yale University.
    3. Perron, Pierre & Vogelsang, Timothy J., "undated". "Level Shifts and Purchasing Power Parity," Instructional Stata datasets for econometrics levshift, Boston College Department of Economics.
    4. Christiano, Lawrence J, 1992. "Searching for a Break in GNP," Journal of Business & Economic Statistics, American Statistical Association, vol. 10(3), pages 237-250, July.
    5. Paul Newbold & Tony Rayner & Neil Kellard, 2000. "Long‐Run Drift, Co‐Movement and Persistence in Real Wheat and Maize Prices," Journal of Agricultural Economics, Wiley Blackwell, vol. 51(1), pages 106-121, January.
    6. Perron, Pierre, 1991. "Test Consistency with Varying Sampling Frequency," Econometric Theory, Cambridge University Press, vol. 7(3), pages 341-368, September.
    7. John C. Robertson & David Orden, 1990. "Monetary Impacts on Prices in the Short and Long Run: Some Evidence from New Zealand," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 72(1), pages 160-171.
    8. Diebold, Francis X. & Rudebusch, Glenn D., 1991. "On the power of Dickey-Fuller tests against fractional alternatives," Economics Letters, Elsevier, vol. 35(2), pages 155-160, February.
    9. Kwiatkowski, Denis & Phillips, Peter C. B. & Schmidt, Peter & Shin, Yongcheol, 1992. "Testing the null hypothesis of stationarity against the alternative of a unit root : How sure are we that economic time series have a unit root?," Journal of Econometrics, Elsevier, vol. 54(1-3), pages 159-178.
    10. Pier Giorgio Ardeni, 1989. "Does the Law of One Price Really Hold for Commodity Prices?," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 71(3), pages 661-669.
    11. Nunes, Luis C. & Newbold, Paul & Chung-Ming Kuan, 1996. "Spurious number of breaks," Economics Letters, Elsevier, vol. 50(2), pages 175-178, February.
    12. Dickey, David A & Fuller, Wayne A, 1981. "Likelihood Ratio Statistics for Autoregressive Time Series with a Unit Root," Econometrica, Econometric Society, vol. 49(4), pages 1057-1072, June.
    13. Schwert, G William, 2002. "Tests for Unit Roots: A Monte Carlo Investigation," Journal of Business & Economic Statistics, American Statistical Association, vol. 20(1), pages 5-17, January.
    14. William O. Tomek, 1994. "Dependence in commodity prices: A comment," Journal of Futures Markets, John Wiley & Sons, Ltd., vol. 14(1), pages 103-109, February.
    15. Rodrigues, Paulo M. M. & Taylor, A. M. Robert, 2004. "Alternative estimators and unit root tests for seasonal autoregressive processes," Journal of Econometrics, Elsevier, vol. 120(1), pages 35-73, May.
    16. Vogelsang, Timothy J & Perron, Pierre, 1998. "Additional Tests for a Unit Root Allowing for a Break in the Trend Function at an Unknown Time," International Economic Review, Department of Economics, University of Pennsylvania and Osaka University Institute of Social and Economic Research Association, vol. 39(4), pages 1073-1100, November.
    17. Vogelsang, Timothy J., 1997. "Wald-Type Tests for Detecting Breaks in the Trend Function of a Dynamic Time Series," Econometric Theory, Cambridge University Press, vol. 13(6), pages 818-848, December.
    18. Leybourne, S J & McCabe, B P M, 1994. "A Consistent Test for a Unit Root," Journal of Business & Economic Statistics, American Statistical Association, vol. 12(2), pages 157-166, April.
    19. Smith, Richard J. & Taylor, A. M. Robert, 1998. "Additional critical values and asymptotic representations for seasonal unit root tests," Journal of Econometrics, Elsevier, vol. 85(2), pages 269-288, August.
    20. Chu, Chia-Shang James & White, Halbert, 1992. "A Direct Test for Changing Trend," Journal of Business & Economic Statistics, American Statistical Association, vol. 10(3), pages 289-299, July.
    21. Busetti, Fabio & Taylor, A. M. Robert, 2003. "Testing against stochastic trend and seasonality in the presence of unattended breaks and unit roots," Journal of Econometrics, Elsevier, vol. 117(1), pages 21-53, November.
    22. Bai, Jushan, 1998. "A Note On Spurious Break," Econometric Theory, Cambridge University Press, vol. 14(5), pages 663-669, October.
    23. Ng, Serena, 1995. "Testing for unit roots in flow data sampled at different frequencies," Economics Letters, Elsevier, vol. 47(3-4), pages 237-242, March.
    24. Perron, Pierre, 1989. "The Great Crash, the Oil Price Shock, and the Unit Root Hypothesis," Econometrica, Econometric Society, vol. 57(6), pages 1361-1401, November.
    25. Choi, In, 1992. "Effects of data aggregation on the power of tests for a unit root : A simulation study," Economics Letters, Elsevier, vol. 40(4), pages 397-401, December.
    26. Elliott, Graham & Rothenberg, Thomas J & Stock, James H, 1996. "Efficient Tests for an Autoregressive Unit Root," Econometrica, Econometric Society, vol. 64(4), pages 813-836, July.
    27. Perron, Pierre, 1990. "Testing for a Unit Root in a Time Series with a Changing Mean," Journal of Business & Economic Statistics, American Statistical Association, vol. 8(2), pages 153-162, April.
    28. Kim, Tae-Hwan & Leybourne, Stephen & Newbold, Paul, 2002. "Unit root tests with a break in innovation variance," Journal of Econometrics, Elsevier, vol. 109(2), pages 365-387, August.
    29. Hall, Alastair R, 1994. "Testing for a Unit Root in Time Series with Pretest Data-Based Model Selection," Journal of Business & Economic Statistics, American Statistical Association, vol. 12(4), pages 461-470, October.
    30. Wang, Dabin & Tomek, William G., 2004. "Commodity Prices And Unit Root Tests," 2004 Conference, April 19-20, 2004, St. Louis, Missouri 19032, NCR-134 Conference on Applied Commodity Price Analysis, Forecasting, and Market Risk Management.
    31. Perron, Pierre & Vogelsang, Timothy J, 1992. "Nonstationarity and Level Shifts with an Application to Purchasing Power Parity," Journal of Business & Economic Statistics, American Statistical Association, vol. 10(3), pages 301-320, July.
    32. Leybourne, Stephen J. & C. Mills, Terence & Newbold, Paul, 1998. "Spurious rejections by Dickey-Fuller tests in the presence of a break under the null," Journal of Econometrics, Elsevier, vol. 87(1), pages 191-203, August.
    33. Perron, Pierre & Vogelsang, Timothy J, 1992. "Testing for a Unit Root in a Time Series with a Changing Mean: Corrections and Extensions," Journal of Business & Economic Statistics, American Statistical Association, vol. 10(4), pages 467-470, October.
    34. Dabin Wang & William G. Tomek, 2007. "Commodity Prices and Unit Root Tests," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 89(4), pages 873-889.
    35. Cuddington, John T & Urzua, Carlos M, 1989. "Trends and Cycles in the Net Barter Terms of Trade: A New Approach," Economic Journal, Royal Economic Society, vol. 99(396), pages 426-442, June.
    36. Marriott, John & Newbold, Paul, 2000. "The strength of evidence for unit autoregressive roots and structural breaks: A Bayesian perspective," Journal of Econometrics, Elsevier, vol. 98(1), pages 1-25, September.
    37. Kenneth A. Foster & Arthur M. Havenner & Allan M. Walburger, 1995. "System Theoretic Time-Series Forecasts of Weekly Live Cattle Prices," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 77(4), pages 1012-1023.
    38. Wang, Dabin & Tomek, William G., 2004. "Commodity Prices And Unit Root Tests," Working Papers 127145, Cornell University, Department of Applied Economics and Management.
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    3. Guillotreau, Patrice & Jiménez-Toribio, Ramón, 2011. "The price effect of expanding fish auction markets," Journal of Economic Behavior & Organization, Elsevier, vol. 79(3), pages 211-225, August.

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