A Novel Efficiency Index for Commodity Futures

Abstract

We re-examine the market efficiency of commodity futures using a new approach that accounts for both time-varying risk premium and conditional heteroscedasticity of spot prices. The conventional market efficiency tests so far in the literature are based on either risk neutral or constant risk premium assumptions as such they are biased towards the rejection of the market efficiency hypothesis especially for commodity futures. The time varying risk premium is estimated using a state space model with a modified Kalman filter. Using a Monte Carlo simulation, we show that the proposed test produces robust and superior results under varying market conditions compared to the conventional approaches. By employing the proposed test we analyse the efficiency of crude oil, corn, copper and gold futures and find that gold futures is inefficient throughout the sample period 2000-2011 while others are efficient especially after the global financial crisis (GFC) in 2008. We also find significant changes in the underlying risk premiums due to the GFC. We extend the analysis to a comprehensive sample of 85 commodities traded on 16 exchanges worldwide and find that efficiency and risk premiums vary across the four market sectors while GFC has caused to increase both efficiency and risk premiums in all markets other than precious metals.