Quantification of the High Level of Endogeneity and of Structural Regime Shifts in Commodity Markets

Abstract

We propose a novel index of short-term endogeneity (or reflexivity) derived by calibrating the Hawkes self-excited conditional Poisson model on empirical time series of trades. The Hawkes model accounts simultaneously for the co-existence and interplay between the exogenous impact of news and the endogenous mechanism by which past trading activity may influence future trading activity. Technically known in the mathematical literature on branching processes as the branching ratio, the reflexivity index is quantified for several commodity futures markets (corn, oil, soybean, sugar, and wheat) and also for a benchmark equity futures market (E-mini S&P 500). Specifically, the reflexivity index is the average ratio of the number of price moves that are due to endogenous interactions to the total number of all price changes, which also include exogenous events. We find an overall increase of the level of short-term endogeneity since the mid-2000s to October 2012, with a typical value nowadays around 0.6–0.7, implying that at least 60–70 per cent of commodity price changes are now due to self-generated activities rather than novel information. Our robustness tests show that the branching ratio provides a ‘pure’ measure of endogeneity that is independent of the rate of activity, order size, volume or volatility. We complement our analysis by relating the endogeneity dynamics of these futures markets to their price dynamics, particularly around the commodity bubble that developed since 2006 and culminated in mid-2008. While our index does not have a long-term memory, interestingly, we find that it can still provide some interesting insights when the mechanisms working at longer time scales cascade down to shorter terms.