On the Comovement of Commodity Prices

We present strong evidence against the excess-comovement hypothesis—that the prices of commodities move together beyond what can be explained by fundamentals. Prior studies employ broad macroeconomic indicators to explain common price movements, and potentially correlated fundamentals are not controlled for. We use inventory and harvest data to fit a partial equilibrium model that more effectively captures the variation in individual prices. The model explains the majority of the comovements among commodities with high price correlation, and all of the comovements among those with marginal price correlation. Common movements in supply factors appear to play an important role in the observed comovements in commodity prices. Copyright 2006, Oxford University Press.

Some further empirical evidence on the impact of oil price changes on petrol prices

This paper analyses the asymmetries in the response of petrol prices to oil price shocks. We show that previous work, based on the determination of asymmetric responses, can be improved upon by allowing for asymmetries in short term dynamics. The paper shows that a significant determinant of the response of petrol prices to oil price changes, is the extent to which petrol price can be seen to have departed from its long run equilibrium level.Petrol Price, Oil Prices, Asymmetric Adjustment, Non-Linearity, Cointegration,

Modelos de cointegração com um ou dois limiares: uma aplicação para o preço do frango inteiro resfriado em mercados atacadistas no Brasil

A maioria dos estudos de integração de mercados que utiliza a técnica de cointegração com threshold não se preocupa em testar qual o número de regimes de ajustamento de preços é o mais adequado. Neste estudo, utiliza-se um procedimento para determinar o número de regimes estatisticamente indicado para diferentes mercados regionais de carne de frango no Brasil, no período de janeiro de 1998 a junho de 2007. Os resultados mostram que, para um grupo de mercados, o modelo com dois regimes é o mais indicado, enquanto para os demais mercados, o modelo com três regimes é o que melhor se ajusta. Constata-se a presença de significativas barreiras à transmissão de choques de preços entre os mercados, o que provavelmente resulta de custos de transação não desprezíveis na comercialização da carne de frango.<br>Most studies about market integration that use threshold cointegration do not usually test the number of regimes of price adjustment. In this study, we use a testing procedure to determine the number of statistically significant regimes for regional markets of poultry in Brazil in the period of January 1998 to June 2007. Results show that, for some markets, two regimes are adequate, whereas for others, the model should have three regimes. We also conclude that there are important barriers to price transmission among the markets which may come from the existence of high transaction costs regarding trades involving poultry

The Performance of Variance Ratio Unit Root Tests Under Nonlinear Stationary TAR and STAR Processes: Evidence from Monte Carlo Simulations and Applications

Variance ratio unit root tests, TAR, STAR, Size distortion, Low power, Yield spread, C12, C22,