The market efficiency hypothesis: The case of coffee and cocoa futures
研究了咖啡和可可期货的市场效率假说，使用2个月和6个月合约的日数据，通过协整检验和误差修正模型发现长期无偏性成立但短期存在偏差。
This study tests the market efficiency hypothesis for coffee and cocoa futures using daily data for contracts with a maturity of 2 and 6 months. The hypothesis is tested sequentially. The first condition is that future spot and futures prices be cointegrated. If this condition is maintained, market efficiency requires the cointegrating vector to support a (0, 1) restriction that can be likened to an unbiasedness condition. Finally, market efficiency imposes zero restrictions on the parameters of the variables expressed in first differences in the specification of the error-correction representation of the relationship between future spot and futures prices. Brenner and Kroner [Brenner, R., Kroner, K., 1995. Arbitrage, cointegration, and testing the unbiasedness hypothesis in financial markets. Journal of Financial and Quantitative Analysis 30, pp. 23-42] argue that the cointegration condition is rarely met in practice. They attribute this outcome to potentially non-stationary net cost-of-carry which would make the parameters of the cointegration relation unstable. It is for this reason that Hansen's tests [Hansen, B.E., 1992. Tests of parameter instability in regressions with /(1) processes. Journal of Business and Economic Statistics 10] about the stability of the parameters in cointegration regressions were used to supplement more traditional cointegration tests. Johansen and Juselius' cointegration tests [Johansen, S., Juselius, K., 1992. Testing structural hypotheses in a multivariate cointegration analysis of the PPP and the UIP for UK, Journal of Econometrics 53] could not reject cointegration for all four contracts while Hansen's Lc test favored cointegration only for the cocoa contracts. Nested and non-nested testing procedures were used to test the (0, 1) restriction on the cointegration vector. Unbiasedness was found to be robust across testing procedures. However, further testing about the specification of the error-correction representation revealed the existence of important short run deviations from unbiasedness. Even though these results hold strictly for a rather limited number of contracts and commodities, they are encouraging for futures markets advocates in developing countries. © 1997 Elsevier Science B.V.