The relationship between the South African Rand and commodity prices: examining cointegration and causality between the nominal classes

Abstract

We employ OLS analysis on a VAR Model to test the “commodity currency” hypothesis of the Rand (i.e. that the currency moves in sympathy with commodity prices) and examine the associated causality using nominal data between 1996 and 2010. We address the question of cointegration using the Engle-Granger test. We find that level series of both assets are difference stationary but not cointegrated. Further, we find the two variables negatively related with strong and significant causality running from commodity prices to the exchange rate and not vice versa, implying exogeneity to the determination of commodity prices with respect to the nominal exchange rate. The strength of the relationship is significantly weaker than other OECD commodity currencies. We surmise that the relationship is dynamic over time owing to the portfolio-rebalance argument and the Commodity Terms of Trade (CTT) effect and in the absence of an error correction mechanism, this disconnect may be prolonged. For commodity and currency market participants, this implies that while futures and forward commodity prices may be useful leading indicators of future currency movements, the price risk management strategies may need to be recalibrated over time. For monetary policy makers, to manage commodity price risk and concentration risk on the country’s exports, we suggest establishment of a selfinsurance scheme such as a Commodity Stabilisation Fund established in Chile in 1985.